Opinion for the court filed by Circuit Judge RADER. Circuit Judge LOURIE dissents in part.
RADER, Circuit Judge.
The United States District Court for the Central District of California denied the appellants’ motion for Judgment as a Matter of Law (JMOL) which sought to overturn the jury verdicts of patent validity and willful infringement. See Union Oil Co. of Cal. v. Atlantic Richfield Co., No. CV-95-2379-KMW, slip op. at 1 (C.D.Cal. Mar. 10, 1998) (Unocal I). In their JMOL motion, the Atlantic Richfield Company and other appellant refiners asserted that Union Oil Company of California’s (Unocal) United States Patent No. 5,288,393 (’393 patent) is invalid under 35 U.S.C. §§ 102 and 112 (1994). The district court also held that Unocal did not commit inequitable conduct before the U.S. Patent and Trademark Office (PTO). See Union Oil Co. of Cal. v. Atlantic Richfield Co., 34 F.Supp.2d 1208, 1222 (C.D.Cal.1998) (Unocal II). Because the appellant refiners did not show a reversible flaw in the jury’s verdict, this court affirms the district court’s denial of JMOL on §§ 102 and 112 issues. Similarly, this court affirms the trial court’s discretionary judgment of no inequitable conduct.1
I.
Unocal owns the ’393 patent, which claims automotive gasoline compositions that reduce automobile tailpipe emissions. Unocal’s original patent application contained 82 claims. As is often the case during the course of prosecution, the inventor added and canceled many claims. Ultimately, 155 claims issued, but Unocal later disclaimed all but the forty-one at issue in this case: claims 20, 53, 54, 56, 57, 71-75, 78, 79, 81, 112-16, 117 (multiply dependent on claims 53, 73, 78, 112, 116, and 125), claim 120 (multiply dependent on claims 55, 78, 79, and 124), claim 121 (dependent on claim 120 and therefore multiply dependent on claims 55, 78, 79 or 124), 125-27, 133-35, 137, 153, and 155. Each claim appears in dependent or multiple [992]*992dependent form, and has from four to six limitations describing ranges for several of the fuel characteristics. Each claim effectively begins either with the preface “[a]n unleaded gasoline fuel suitable for combustion in an automotive engine” or “[a]n unleaded gasoline fuel suitable for combustion in a spark ignition automotive engine.” As an example, Claim 117, as dependent upon claim 116, states:2
117. [An unleaded gasoline fuel. suitable for combustion in an automotive engine, said fuel having a Reid Vapor pressure no greater than 7.0 psi, and a 50% D-86 distillation point no greater than 200° F., and a 90% D-86 distillation point no greater than 300° F., and a paraffin content greater than 85 volume percent, and an olefin content less than 4 volume percent] wherein the maximum 10% distillation point is. 158° F (70° C.).
’393 patent, col. 24,11. 24-27.
As illustrated above, the claims do not describe each gasoline product in terms of molecular structures or lists of ingredients. Instead, the claims specify the chemical properties of the gasolines, reflecting the way oil refiners formulate gasoline. When oil refiners formulate new gasoline products, they do so by mixing petroleum stocks. Different stocks have different properties that are known to oil refiners. The record shows that oil refiners of ordinary skill in the art change the chemical properties of gasoline by varying the proportions of different petroleum stocks. Thus the claims which define the invention in terms of various characteristics also inform those of skill in the art of the composition of the claimed gasoline fuels.
Unocal researched extensively the production of automotive gasoline with reduced combustion emissions. Unocal’s scientists, Drs. Jessup and Croudace, ultimately filed' a patent application based on their findings. Their research taught ways to produce cleaner gasoline by varying the following chemical properties in automotive gasolines: Reid Vapor Pressure (RVP), TIO, T50, T90, Olefins, Paraf-fins, Aromatics,3 and Octane.
RVP measures the partial pressure of a gasoline sample when heated to 100° F in a sealed container. See id. at col. 18, 11. 43-47. TIO, T50 and T90 are abbreviations for percentage distillation points, as measured according to an industry standard procedure . called “D-86.” Each corresponds • to the temperatures at which a given percentage of the gasoline sample enters a gaseous phase under specific experimental conditions. Thus, T10 is the 10% D-86 distillation point; T50 the 50% D-86 distillation point; and T90 the 90% D-86 distillation point. The olefins value describes the percentage of the gasoline comprised of olefins measured by volume. Olefins, otherwise known as alkenes, are open-chain hydrocarbons that contain at least one double bond. The paraffins value describes the percentage of the gasoline comprised of paraffins measured by volume. Paraffins, otherwise known as al-kanes, are open-chain hydrocarbons that contain only single bonds. The aromatics value describes the percentage of the gasoline comprised of aromatics measured by volume. Aromatics, are compounds whose properties resemble those of 6-carbon ring molecules that have an average of three intra-ring carbon-carbon double bonds (i.e., benzene). Octane, as used in the ’393 patent, describes the knocking or detonation characteristics of a gasoline sample as compared with a reference fuel. The octane value is derived by testing gasoline in a special engine under specified experimental conditions, and comparing those results to identically tested reference blends of Isooctane and n-heptane.
[993]*993Drs. Jessup and Croudace sought to reduce the levels of carbon monoxide (CO), nitrous oxide (N0X), and hydrocarbons (HC) emitted from automobile tailpipes. After considerable experimentation, Drs. Jessup and Croudace discovered relationships between the various petroleum characteristics described above and tailpipe emissions. Drs. Jessup and Croudace then patented their innovative fuel compositions, describing the new compositions by their characteristics.
The specification of the ’393 patent describes relationships among automotive gasoline characteristics and fuel emissions, including the following:
1. Decreasing RVP is of primary importance, and decreasing TIO and olefin content are of secondary importance for reducing NOx emissions. See ’393 patent, col. 2, 11. 21-29.
2. Decreasing T50 is of primary importance for reducing CO and HC emissions. See id. at 11. 7-11.
3. Increasing paraffin content and decreasing T50 are most effective for reducing CO emissions. See id. at col. 6,11. 12-28.
4. Decreasing both olefin content and RVP are most effective for reducing NOx emissions. See id. at 11. 28-31.
5. HC emissions are most practically reduced by decreasing olefins and/or T50. See id. at 11. 46-50.
6. Any combination of the eight characteristics can be increased or decreased as described, and that the greater any individual characteristic is changed in the directions indicated, the better the result. See id. at col. 15,11. 20-28.
The specification also provides specific numerical ranges for each characteristic. For example, the specification teaches:
1.CO and HC emissions can be minimized by reducing T50 below 215° F, preferably below 195° F. See id. at col. 2,11. 7-20.
2. NOx emissions can be minimized by (a) decreasing RVP to 8.0 psi or less (preferably below 7.0 psi); (b) decreasing olefins below 15% (preferably to essentially zero); or (c) decreasing T10 below 140° F. See id. at 11. 21-34.
3. The best NOx reductions are obtained when the olefins are below 15%, RVP is ,7-5 psi or less, and T10 is below 140° F. See id. at 11. 44-50.
4. All three pollutants are reduced when T50 is 215° F or less and RVP is 8.0 psi or less, with greater reductions when olefins are below 10% or . T10 is below 140° F, and still greater reductions when both olefins and T10 are reduced. See id. at 11. 54-64.
5. Further pollution reductions are possible when T50 is below 195° F, olefins are below 5% (preferably at essentially zero), T10 is below 120° F, and/or when RVP is below 7.0 psi. See id. at 1. 64 — col. 3,1. 3.
Elsewhere the specification describes the optimal ranges for five of the eight fuel characteristics in similar "terms.
The specification also states that the gasolines are preferably unleaded, have an octane rating of at least 90, and fall most preferably within one or more of five volatility classes in American Society for Testing and Materials (ASTM) publication D4814-89 (included in Table 1 -of the patent). See id. at col. 4, 1. 66 — col. 5., 1. 13. Beyond.the optimal ranges for individual characteristics, the ’393 patent also discloses preferred fuel mixtures. In sum, the ’393 disclosure describes with detail the benefits and methods of varying gasoline characteristics. The specification describes 1) the relationships among the eight individual fuel characteristics and CO, NOx, and HC emissions, 2) characteristics most important for emissions, and 3) specific desirable ranges for RVP, T10, T50, olefins, paraffins, and aromatics.
[994]*994The appellant refiners originally sued Unocal in district court, seeking a declaratory judgment to invalidate the ’393 patent. Unocal counterclaimed, alleging willful infringement of the ’393 patent. The district court then construed the claims of the ’393 patent, effectively converting the refiners’ declaratory judgment action into an infringement defense. Then the district court tried those invalidity issues to a jury. During forty-nine days of trial, the jury heard the testimony of numerous witnesses and considered hundreds of exhibits and demonstrations. See Unocal I, slip op. at 6. At the close of all evidence, the district court properly instructed the jury on the law, and presented the jury with a special verdict form. . The verdict form required the jury to decide validity under § 102 and § 112 separately for each of the forty-one asserted claims. With respect to the § 112 questions, the trial court asked the jury to consider the ’393 patent’s specification, including the original claims of the application, as filed. See Northern Telecom, Inc. v. Datapoint Corp., 908 F.2d 931, 938, 15 USPQ2d 1321, 1326 (Fed.Cir.1990) (“The original claims as filed are part of the patent specification.”). In total, the trial court’s special verdict form asked the jury 223 individual questions. After thirteen days of deliberation, the • jury returned and answered affirmatively that sufficient written description supported each of the forty-one asserted claims, and that none was anticipated under § 102.
The appellant refiners then moved the district court to overturn the jury’s verdict with a motion for JMOL based on anticipation, obviousness, and lack of written description. After reviewing arguments of both parties and the record, the district court found that “substantial evidence exists in the record regarding the written description to support the verdict that Drs. Jessup and Croudace had possession of the claimed subject matter.” Unocal I, slip op. at 6. The district court similarly considered and rejected appellant refiners’ arguments on anticipation and obviousness. See id. at 3-5.
The appellant refiners also argued that the ’393 patent was unenforceable for inequitable conduct. The district court tried that issue itself and held that the refiners did not meet their-burden of showing inequitable conduct by clear and convincing evidence. See Unocal II, 34 F.Supp.2d at 1222. The district court found the case exceptional, and therefore also awarded attorney fees to Unocal under 35 U.S.C. § 285 (1994).
The appellant refiners now appeal the district court’s denial of JMOL on anticipation and written description. They also appeal the district court’s inequitable-conduct decision.
II.
This court reviews the district court’s JMOL ruling after a jury verdict by reapplying the district court’s own standard. See Applied Med. Resources Corp. v. United States Surgical Corp., 147 F.3d 1374, 1376, 47 USPQ2d 1289, 1290 (Fed.Cir.1998). Thus, to prevail on appeal, the appellant refiners must show that substantial evidence does not support the jury’s factual findings or that the district court erred in applying the law. See id.
A district court may overturn a jury’s verdict on a motion for JMOL only if, upon the record before the jury, reasonable persons could not reach the verdict returned by that jury. See Perkin-Elmer Corp. v. Computervision Corp., 732 F.2d 888, 893, 221 USPQ 669, 673 (Fed.Cir.1984). This court must consider the evidence of record in the light most favorable to Unocal, drawing all reasonable inferences in its favor, without disturbing the jury’s credibility determinations or substituting this court’s resolutions of conflicting evidence for those of the jury. See Applied Med., 147 F.3d at 1376-77.
A.
This court requires that a party seeking to invalidate a patent under § 102 [995]*995show that the allegedly invalidating prior art contains “each and every element of [the] claimed invention.” Lewmar Marine, Inc. v. Barient, Inc., 827 F.2d 744, 747, 3 USPQ2d 1766, 1767 (Fed.Cir.1987). To prevail on anticipation at trial, the refiners had to prove their case by clear and convincing evidence. See Verdegaal Bros. v. Union Oil Co., 814 F.2d 628, 631, 2 USPQ2d 1051, 1052-53 (Fed.Cir.1987). The law imposes this high burden because Unocal’s patent, like any issued patent, enjoys a presumption of validity. See id.
This court reviews a finding of anticipation as a question of fact. See In re Graves, 69 F.3d 1147, 1151, 36 USPQ2d 1697, 1700 (Fed.Cir.1995). Therefore, on appeal, this court must affirm the district court’s denial of JMOL on anticipation if substantial evidence supports the jury’s verdict that the cited prior art did not anticipate the claims.
“The first step in any invalidity ... analysis is claim construction.” See Rockwell Int’l Corp. v. United States, 147 F.3d 1358, 1362, 47 USPQ2d 1027, 1029 (Fed.Cir.1998). Claim construction is a question of law, which this court reviews without deference. See Georgia-Pacific Corp. v. United States Gypsum Co., 195 F.3d 1322, 1330, 52 USPQ2d 1590, 1597 (Fed.Cir.1999). “In claim construction the words of the claims are construed independent of the accused product, in light of the specification, the prosecution history, and the prior art.... [T]he construction of claims is simply a way of elaborating the normally terse claim language[] in order to understand and explain, but not to change, the scope of the claims.” Scripps Clinic v. Genentech, Inc., 927 F.2d 1565, 1580, 18 USPQ2d 1001, 1013 (Fed.Cir.1991) (internal quotation marks omitted).
The claims of the ’393 patent recite either “[a]n unleaded gasoline suitable for combustion in an automotive engine” or “[a]n unleaded gasoline fuel suitable for combustion in a spark ignition automotive engine.” Thus, the ’393 patent claims compositions of matter. The scope of these composition claims cannot, as the appellant refiners argue, embrace only certain uses of that composition. See In re Spada, 911 F.2d 705, 708, 15 USPQ2d 1655, 1657 (Fed.Cir.1990). Otherwise these composition claims would mutate into method claims. The district court correctly applied this principle, refusing to narrow the scope of the claimed compositions to specific uses.
The district court read each claim in light of the specification, and concluded that the claims cover “fuels that will regularly be used in autos, not that conceivably could be.” Union Oil Co. of Cal. v. Atlantic Richfield Co., No. CV-95-2379-KMW, slip op. at 7 (C.D.Cal. May 19, 1997) (Unocal III). The district court thus construed the claims to cover only a narrow class of fuel compositions, namely only standard automotive gasoline. The district court correctly excluded .from claim scope a broader class of petroleum formulations' such as aviation fuels or racing fuels. The claim language confirms the district court’s reading of the claims to cover mass market automotive gasoline. The claim language specifies fuels for an “automotive engine,” not an aviation engine. See, e.g., ’393 patent, col. 18, 1. 65. Moreover the explicit reference to “unleaded gasoline” again invokes standard automotive fuels, rather than specialized fuels. See, e.g., id. at col. 18,1. 64.
The district court’s interpretation also finds extensive support in the specification. The patentees described the problem that their invention addressed: [996]*996Id. at col. 1,11. 9-16. Similarly, the paten-tees describe their testing procedures and results in the specification. Specifically, the patentees used ordinary passenger automobiles in their tests. The ’393 patent records the results of testing certain fuels in a 1989 Oldsmobile Calais, a 1988 Oldsmobile 98, a 1985 Ford Tempo, a 1990 Lincoln, a 1984 Chevrolet Caprice, a 1988 Honda Accord, a 1989 Ford Taurus, a 1990 Plymouth Shadow, a 1985 Chevrolet Suburban, and a 1990 Toyota Camry. See id. at fig. 9. None of these are aviation or racing vehicles.
[995]*995One of the major environmental problems confronting the United States and other countries is atmospheric pollution (i.e., “smog”) caused by the emission of gaseous pollutants in the exhaust gases from automobiles. This problem is especially acute in major metropolitan areas, such as Los Angeles, Calif., where the atmospheric conditions and the great number of automobiles account for aggravated air pollution.
[996]*996Similarly, another passage provides context for the trial court’s claim construction. The patentees describe their choice of test vehicles as follows:
A total of 22 different unleaded gasoline fuels was tested in a 1988 Oldsmobile Regency 98 automobile equipped with a 3800 cc V-6 engine. This automobile was selected because it represented a high sales volume product with close to the current state-of-the-art emission technology. • ,
Id. at col. 7, 11. 61-6. The patentees tailored their research and their patent to ordinary fuels for use in standard passenger cars. Thus, the claim language, further informed by the specification, shows that the district court correctly read the claims to cover ordinary automotive fuel.
Because the ’393 patent covers only standard automotive fuel, the district court correctly determined that specialty fuels within other limitations of the claims do not anticipate under 35 U.S.C. § 102. In other words, the aviation and racing fuels that allegedly invalidate the ’393 claims do not anticipate because they do not contain each and every limitation of the claims. See Verdegaal, 814 F.2d at 631. Specifically, this alleged prior art does not include the limitation of being a standard automotive fuel composition.
Moreover, the record does not show that the aviation and racing fuels otherwise have the claimed characteristics of the particular standard automotive fuels recited in the ’393 patent. While the record shows that some properties of the aviation and racing fuels coincide with the properties of the ’393 patent’s claims, the record does not show- the presence of each and every limitation. An expert for the refiner appellants stated that the allegedly anticipatory Phillips B-35 racing fuel “is very different from typical [automotive fuel].” Tr. at 4782. When asked, “Is Unocal unleaded racing gasoline very different from typical motor gasoline?”, the expert again answered “Yes.” Id. at 5047. This expert similarly answered “yes” when questioned about whether the asserted aviation fuels were “very different” from typical motor gasoline. See id. at 5060.
The district court did not err in construing the claims of the ’393 patent. Furthermore the record does not show each and every element of the asserted claims of the ’393 patent present in any single prior art reference. Therefore, this court affirms the district court’s denial of JMOL on anticipation.
. B.
The first paragraph of § 112 states that: “The specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same.” 35 U.S.C. § 112. In written description cases, “[t]he primary consideration is factual and depends on the nature of the invention and the amount of knowledge imparted to those skilled in the art by the disclosure.” In re Wertheim, 541 F.2d 257, 262, 191 USPQ 90, 96 (CCPA 1976) (emphasis added). This court reviews a jury’s factual findings for substantial evidence. See B. Braun Med., Inc. v. Abbott Labs., 124 F.3d 1419, 1423, 43 USPQ2d 1896, 1899 (Fed.Cir.1997).
[997]*997The written description requirement does not require the applicant “to describe exactly the subject matter claimed, [instead] the description must clearly allow persons of ordinary skill in the art to recognize that [he or she] invented what is claimed.” In re Gosteli 872 F.2d 1008, 1012, 10 USPQ2d 1614, 1618 (Fed.Cir.1989) (citations omitted). Thus, § 112, ¶ 1 ensures that, as of the filing date, the inventor conveyed with reasonable clarity to those of skill in the art that he was in possession of the subject matter of the claims. See Vas-Cath Inc. v. Mahurkar, 935 F.2d 1555, 1563-64, 19 USPQ2d 1111, 1117 (Fed.Cir.1991).
In the course of the lengthy jury trial, the district court heeded this court’s counsel to use special verdicts in complex cases. See Comark Communications, Inc. v. Harris Corp., 156 F.3d 1182, 1189 n. 1, 48 USPQ2d 1001, 1006 n. 1 (Fed.Cir.1998). The district court presented the jury with a verdict form asking it to decide separately whether each of the claims met the written description requirement. Following these instructions, the jury returned its verdict answering affirmatively forty-one separate times that sufficient written description supported each of the asserted claims.
After the jury’s verdict, the appellant refiners renewed their motion for JMOL to overturn the jury’s verdict. See Fed.R.Civ.P. 50(b). The district judge then reconsidered the patent documents independently in light of all the evidence and denied the JMOL motion, thus upholding the jury’s verdicts. Like the district court, this court must accord deference to the jury findings on written description. This court will not substitute its judgment for that of the fact finder. See General Electro Music Corp. v. Samick Music Corp., 19 F.3d 1405, 1412, 30 USPQ2d 1149, 1155 (Fed.Cir.1994).
On the record in this appeal, substantial evidence amply supports the jury’s findings and the trial judge’s JMOL ruling. The ’393 patent teaches the effects of varying the properties of automotive gasolines to reduce harmful tailpipe emissions. In the art of gasoline production, skilled refiners obtain raw petroleum products and mix them together to achieve a desired product. Each product is the mixture of many chemicals in varying proportions. The ’393 patent teaches that changes in the proportions of different hydrocarbon-containing streams mixed to produce gasoline with specific properties reduces the amount of NOx, CO, and hydrocarbons emitted from an automobile engine. Varying one or more properties in turn effects other properties of a gasoline product. Therefore, the patent claims its inventive products in terms of ranges of chemical properties, which work in combination with ranges of other chemical properties to produce a gasoline that reduces emissions.
Appellant refiners assert that the specification does not describe the exact chemical component of each combination that falls within the range claims of the ’393 patent. However, neither the Patent Act nor the case law of this court requires such detailed disclosure. See In re Hayes Microcomputer Prods., Inc., 982 F.2d 1527, 1533, 25 USPQ2d 1241, 1245 (“[The applicant] does not have to describe exactly the subject matter claimed.”); Vas-Cath, 935 F.2d at 1566 (“ranges found in applicant’s claims need not correspond exactly to those disclosed in [the specification]; issue is whether one skilled in the art could derive the claimed ranges from the [] disclosure.”). Rather, the Patent Act and this court’s case law require only sufficient description to show one of skill in the refining art that the inventor possessed the claimed invention at the time of filing.
Drs. Jessup and Croudace described their invention in terms of ranges. That form of description does not offend § 112, ¶ 1. In fact, this invention lends itself to description in terms of ranges and variance of those ranges to achieve particular properties of the gasoline products. The inquiry for adequate written description [998]*998simply does not depend on a particular claim format, but rather on whether the patent’s description would show those of ordinary skill in the petroleum refining art that the inventors possessed the claimed invention at the time of filing.
In this case, the patent teaches one of ordinary skill that reducing T50 progressively reduces CO and hydrocarbons; reducing olefins progressively reduces NOx and hydrocarbons; increasing paraffins progressively reduces CO and NOx; and so forth with several other relationships. Then the patent claims ranges for these properties that provide cleaner gasoline emissions. The Background and Abstract portions of the specification discuss thoroughly the claimed ranges and the combinations of multiple properties.
For example, the written description supporting a single claim - claim 117— follows:
Claim limitation Support in ’393 patent
T50 at < 200° Col. 14, II. 9-15: “no greater than 210° F.„ .. but preferably .. . less than 200° F”
RVP at s 7.0 psi Col. 14, II. 36-40: “Reid Vapor Pressure specification of 8.0 psi.. , even more preferably no greater than 7.0 psi.
Olefin at < 4.0 volume percent Col. 14, II. 23-30: “varying the olefin content, this value is generally maintained less than 15 volume percent, with decreasing values providing progressively improved results. Thus, it is contemplated that each unit reduction, e.g., to values below.. ■ 4... providing progressively better results.,,.”
Paraffin at > 85 volume percent Col. 14, II. 49-64: “progressively increasing the paraffin content progressively decreases the CO emitted. Accordingly ... the paraffin content would be increased to ... and most preferably of all above 85 volume percent.
T90 at < 300° claimed exactly in original claim 294
T10at<; 158° Col. 5, lis. 6-30: Table 1 shows maximum T10 distillation temperatures for all five volatility classes at 158 or below._
(Emphasis added.)
The specification further guides the skilled artisan in combining the above properties: “It will also follow that one can increase or decrease any combination of the eight properties listed above, i.e., at least two, at least three, at least four, etc., of the properties can be increased or decreased in the direction indicated above, as well as all eight.” ’393 patent, col. 15, 11. 20-25. The record of the trial contains testimony and exhibits showing in similar terms the written description and support for each of the forty-one claims.
To reiterate, this court supplies the written description supporting another claim, claim 125, as follows:
[999]*999Claim limitation Support in *393 patent
T50 at < 205° Col. 2, II. 17-18: “Preferred fuels have a 50% D-86 Distillation Point of 205a F. (96.1° C) or less.”
RVP at < 7.0 psi Col. 14, II. 36-40: “Reid Vapor Pressure specification of 8.0 psi.. . even more preferably no greater than 7.0 psi...
Olefin at < 6.0 volume percent Col. 14, II. 23-30: “varying the olefin content, this value is generally maintained less than 15 volume percent, with decreasing values providing progressively improved results. Thus, it is contemplated that each unit reduction, e.g., to values below... 6.. ■ providing progressively better results....”
Paraffin at> 75 volume percent Col. 14, II. 49-59: “progressively increasing the paraffin content progressively decreases the CO emitted. Accordingly , . . the paraffin content would be increased to . . . [and] even more preferably above 75 volume percent..._
(Emphasis added.)
Beyond this evidence from the patent itself, skilled refiners testified that the specification taught them that the inventor possessed the emission-reducing gasolines at the time of filing. For example, when questioned, Richard Stellman, an expert in the field, stated:
Q: Does the patent teach one of ordinary skill in the art such as yourself to alter two or more of the properties in a particular - in the prescribed fashion in order to affect all three of the criteria pollutants?
A: Yes, it does.
Q: And does the patent set forth values from which one of ordinary skill in the art can practice the invention? A: Yes, it does.
Tr. at 2515.
The patent unmistakably informs skilled refiners to increase or decrease the various components to arrive at preferred combinations. In fact, the written description usually labels both preferred and most preferred levels within each range. Skilled refiners testified that they knew the composition of the claimed combinations based on this written description. Contrary to appellant refiners’ arguments to this court, the record shows that refiners of ordinary skill understood and applied the ’393 patent’s teachings. In sum, the record shows that the inventors possessed the claimed invention at the time of filing in the assessment of those of ordinary skill in the petroleum refining art.5 Moreover, the jury in this case reached the same conclusion as a matter of fact — a proposition that this court cannot disturb on this record which supplies substantial evidence to support that finding.
The appellant refiners attempt to rescue their written description argument by focusing on the T90 levels cited in claims 74, 81, 116, 117, and 127. Appellant refiners allege that the “specification provides no specific T90 values ... [and that although five of the original application claims recited combinations including a T90 limitation, they bear no resemblance to the remaining claims with T90 limitations.” Appellants’ Br. at 46. Appellant refiners misapprehend the teachings of T90 levels. The ’393 [1000]*1000patent teaches that lowering the T90 distillation point below prior art standards for automotive gasolines creates the desired effect. See ’393 patent, col. 2, 1. 1. The standards set forth in Table 1 of the ’393 patent describe the ASTM standards for gasolines that have T90 distillation points between 365 and 374° F. The T90 distillation points in the originally filed claims were less than or equal to either 315 or 300° F, thus substantially lower than in the prior art gasolines. The claimed ranges of the originally filed claims are the same as those set forth in the six claims of the issued ’393 patent that contain T90 limitations. In other words, the disclosure at the time of filing taught one of skill in the art that the inventors possessed the subject matter of the later claims. Even if appellant refiners’ argument were correct, that analysis only addresses the validity of five claims, leaving the remaining thirty-six claims.
Appellant refiners argue that In re Ruschig, 54 C.C.P.A. 1551, 379 F.2d 990, 154 USPQ 118 (CCPA 1967), supports their argument. This court’s predecessor discussed in Ruschig whether a claim for a particular pharmaceutical compound copied into a patent application for the purposes of provoking an interference was adequately supported by the written description of a class of compounds. Rus-chig is different than this case for several reasons. First, the Ruschig case involved a copied claim (another inventor’s claim copied into Ruschig’s application), which did not find support in Ruschig’s application because Ruschig had invented and disclosed a broad set of the compounds that was similar, but not entirely within the scope of the claim. Because another inventor, not Ruschig, drafted the claim at issue to fit another specification, it is not surprising that the disputed claim did not find support in Ruschig’s specification, even though the inventions were similar. In this case however, the claims, although amended in the course of prosecution, were drawn to the inventions of Jessup and Croudace, who drafted the claims with support from their own specification.
Second, as this -court’s predecessor explained in distinguishing Ruschig in another case involving ranges:
If lack of literal support alone were enough to support a rejection under § 112, then the statement of In re Lukach ... that “the invention claimed does not have to be described in ipsis verbis in order to satisfy the description requirement of § 112,” is empty verbiage.
Wertheim, 541 F.2d at 265. As in this case, in Wertheim the asserted claims covered a range (“solids level of at least 35%”), id. at 258, whereas the specification disclosed a broader range (“concentrated ... until a concentration of 25 to 60% solid matter is reached”), id. at 262 (internal quotation marks omitted). In Wertheim the CCPA held that the specification supported the claimed range, even though the precise range of the claim was not repeated verbatim in the specification, as the dissent in this case would appear to require. In so holding, the court cautioned that it would “let form triumph over substance” if it allowed the written description requirement to eviscerate claims that are narrowed during prosecution, simply because the patent applicant broadly disclosed in the original patent application but then narrowed his claims during prosecution. See id. at 263. Additionally, Wer-theim reiterates the often cited rule that written description questions are intensely factual, and should be dealt with on a case-by-case basis, without the application of wooden rules. See id. at 262. Thus, Wer-theim fully supports the result in this case and limits the applicability of Ruschig.'
Our predecessor court in Ruschig expressed concern over the extent to which the patentee relied on variables in describing structures, leading that court to explain that rather than blaze marks on trees, the patentee had simply provided the public with a forest of trees. Artisans skilled in petroleum refining, in contrast, [1001]*1001are aware of the properties of raw petroleum sources and know how to mix streams of such sources to achieve a final product with desired characteristics. Thus the patentee in this case taught the desired characteristics of the final automotive fuels, realizing that those of skill in this art know that those characteristics define the claimed products.
A closer case for assessing the facts of written description in these forty-one verdicts — one which dealt with ranges and combinations — is Ralston Purina Co. v. Far-Mar-Co, Inc., 772 F.2d 1570, 1575, 227 USPQ 177, 179 (Fed.Cir.1985). In Ralston, a case in which this court applied the less deferential clear error standard appropriate for this court’s review of bench verdicts, this court noted that the ranges in applicant’s claims need not correspond exactly to those disclosed in the parent application. See id. at 1575. Rather, this court clarified that the issue is whether one of skill in the art could derive the claimed ranges from the parent’s disclosure. See id.; see also Vas-Cath, 935 F.2d at 1566 (holding that the district court erred in “applying a legal standard that essentially required the drawings of the ’081 design application to necessarily exclude all diameters other than those within the claimed range.”). Because of the fact-sensitive nature of the written description inquiry, this court has often warned against misapplication of precedents in this area. See Vas-Cath, 935 F.2d at 1562 (citing In re Driscoll, 562 F.2d 1245, 1250, 195 USPQ 434, 438 (COPA 1977)). This case illustrates the reason for that warning. Ralston governs this case.
The written description requirement does not require identical descriptions of claimed compounds, but it requires enough disclosure in the patent to show one of skill in this art that the inventor “invented what is claimed.” Vas-Cath, 935 F.2d at 1563. On this precise question the jury received many days of testimony, heard from skilled refiners, reviewed graphs and claim charts, and examined the patent documents as guided by those skilled in the art. Indeed the district court, which also heard all the evidence from those of skill in the art, stated: “[T]he Court finds that substantial evidence exists in the record regarding written description to support the verdict that Drs. Jessup and Croudace had possession of the claimed subject matter.” Unocal I, slip op. at 6. This court agrees. Because the record shows substantial evidence of adequate written description for each claim as the jury found, this court affirms.
III.
Applicants for U.S. patents and their representatives before the PTO are subject to a duty of candor, good faith and honesty in their prosecution of patent applications. See 37 C.F.R. § 1.56 (1999). “A breáeh of this duty constitutes inequitable conduct.” Molins PLC v. Textron, Inc., 48 F.3d 1172, 1178, 33 USPQ2d 1823, 1826 (Fed.Cir.1995). If a court determines that a patentee has engaged in inequitable conduct, the court must consider whether, as a matter of equity, the patent should be deemed unenforceable. See LaBounty Mfg., Inc. v. ITC, 958 F.2d 1066, 1070, 22 USPQ2d 1025, 1028 (Fed.Cir.1992). Because as the name suggests, inequitable conduct is an equitable issue, this court reviews such determinations for an abuse of discretion. See Kingsdown Med. Consultants, Ltd. v. Hollister Inc., 863 F.2d 867, 876, 9 USPQ2d 1384, 1392 (Fed.Cir.1988) (en banc in relevant part). Moreover this court will not disturb the district court’s factual determinations of materiality and intent without a “definite and firm conviction that a mistake has been committed.” Id.
In this case, the district court issued a thorough and well reasoned opinion that shows consideration of the fundamental issues of inequitable conduct. Specifically, the district court noted that the allegedly withheld test data would not have been material to the patentability of the claims. [1002]*1002See Molins, 48 F.3d at 1179. The district court also found no intent to deceive by withholding the disputed test records, but instead determined that Unocal acted in good faith during the prosecution. This court detects no clear error in these findings and no abuse of discretion in the district court’s determination of no inequitable conduct.
IV.
Because the record contains substantial evidence to support the jury’s verdicts of no anticipation and sufficient written description, this court affirms the district court’s denial of JMOL. Similarly, this court affirms the district court’s inequitable conduct determination.
COSTS
Each party shall bear its own costs.
AFFIRMED.