BROWNING, Circuit Judge:
This is an appeal by Paul Lessig from a judgment entered on a jury verdict in a suit for damages brought by Lessig under Section 4 of the Clayton Act,1 alleg[463]*463ing injury from violations by Tidewater Oil Company of Sections 1 and 2 of the Sherman Act2 and Section 3 of the Clayton Act.3 We conclude that reversible error occurred in instructing the jury, and remand for new trial.
Tidewater entered into a service station lease and dealer contract with Lessig November 15, 1955, and cancelled both May 15, 1958. The theory of Lessig’s ease was that during this period Tidewater violated the antitrust laws (1) by fixing the prices at which its dealers resold gasoline, and (2) by imposing upon its dealers a system of exclusive dealing and tying arrangemenTs“m''tEe_ purcTiiise of petroleum "products, batteries,, and those automotive accessories _which were sold or sponsored by Tidewater, and that Lessig was injured thereby.
I
Resale Price Maintenance
A. Sufficiency of evidence of violation
Lessig offered evidence of the following circumstances in support of his allegation that Tidewater conspired, or created a combination, to control the price at which its dealers resold gasoline.4
Tidewater required its dealers to purchase their estimated total requirements of gasoline from Tidewater at prices “posted by seller at the time and place of delivery.” ’ It steadily increased the wholesale or tank-wagon price charged dealers during the relevant period, though the retail price dropped on several occasions. When the retail price went down, Tidewater extended “dealer-aid” in the form of a rebate from the tank-wagon price. When retail prices went up, the rebate was diminished or withdrawn. Payment of “dealer-aid” was conditioned upon adherence by the dealer to resale prices stipulated by Tidewater.
By maintaining, or increasing, the wholesale price when the retail price declined, Tidewater brought pressure upon dealers to accept “dealer-aid” and the accompanying condition requiring resale price maintenance. In addition, Tidewater’s representatives checked the prices at which dealers sold their gasoline, told dealers the price changes they were to make, changed prices posted on their pumps, placed price signs on the station premises reflecting the new price, and threatened to terminate and terminated dealers’ leases and contracts if dealers’7] did not comply with suggested price changes. Lessig was given notice ofj termination of his lease and contract three days after he refused to reduce his resale -price when Tidewater’s district sales manager told him it was two cents too high.
From this evidence the jury could conclude that Tidewater entered into agreements with its dealers fixing [464]*464resale prices, thus contracting and conspiring in violation of Section 1 of the Sherman Act, or, alternatively, that Tidewater secured dealer adherence to resale prices by a coercive scheme not limited to refusals to deal announced in advance, thus creating a combination in violation of Section l.5
B. Sufficiency of evidence of damage
The evidence supporting Lessig’s claim of injury prior to the termination of his lease and contract from Tidewater’s resale price-fixing activities was not strong. However, the jury could readily infer that Tidewater terminated its business relationship with Lessig because he failed to adhere to the resale price-fixing scheme. Cancellation of Lessig’s lease and dealer contract in such circumstances would be unlawful, though in exercise of a right expressly granted Tidewater by the lease and contract6 Lessig could claim compensation for the resulting loss, including reasonably anticipated future profits,7 and there was evidence from which the jury could find that such loss occurred.
C. Alleged error in instructions
Tidewater makes the threshold contention that review of many of Lessig’s numerous claims of error is barred by Lessig’s failure properly to present his [465]*465objections at trial. This may be true of some specifications, but that we need not decide. Lessig did properly present and preserve an objection to what we believe was reversible error in instructing the jury as to damages.
Lessig tendered to the court a proposed instruction concerning his right to recover reasonably anticipated future profits lost as a result of the cancellation of his lease and contract.8 The instruction was not given, and Lessig made timely objection. The omission was error.9 The error was prejudicial since the jury was instructed in detail as to Lessig’s right to recover profits lost during his occupancy of the station, and therefore might have concluded that he could recover only on this theory.10 Such a misconception could have led to the verdict adverse to Lessig, for while Lessig’s proof of causal connection between the alleged violation and the lease cancellation was substantial and direct, his proof of loss of profits from Tidewater’s conduct during his occupancy of the station was, as we have said, relatively meager and tenuous.
Reversal is thus required,11 and we consider only those remaining assignments of error pertinent to a new trial and ignore Lessig’s failure to comply with Rule 51 of the Federal Rules of Civil Procedure and other procedural obstacles which would ordinarily preclude review of some of the matters discussed.
Lessig argues that the trial court should have instructed the jury that Tidewater’s conduct relating to resale price maintenance violated the Sherman Act as a matter of law. The instruction was properly refused. Tidewater did not concede that “dealer-aid” was conditioned on dealer adherence to its stipulated resale prices. Its officials testified that “dealer-aid” was given whenever the prevailing retail price in a particular area fell below the level at which Tidewater’s dealers could pay the posted wholesale price and retain.a fair margin of profit; and they insisted that each dealer, though receiving the rebate, was nonetheless free to meet the prevailing retail price or not as he saw fit. The jury was entitled to accept this explanation, and reject the contrary evidence.12
[466]*466We agree with Lessig, however, that the instructions given did not adequately inform the jury of the theory underlying the price-fixing aspect of his case. They did not clearly state in terms of the specific facts of the case:13 (1) that Lessig need not prove an express agreement to maintain resale prices, but was entitled to prevail, assuming injury, if he established tacit agreements by circumstantial evidence; and (2) that Tidewater could not lawfully go beyond refusals to deal, announced in advance, to secure adherence to resale prices, .and Lessig was entitled to prevail, assuming injury, if he established that Tidewater exceeded this limitation in the respects indicated by Lessig’s evidence, outlined above.
The instructions on this phase of the case were objectionable in another respect. Lessig testified in detail regarding a conversation with Tidewater’s district sales manager immediately preceding receipt by Lessig of notice of the cancellation of his lease and contract. With apparent reference to this conversation, the court instructed the jury “that it was not unlawful for Tidewater to tell Mr. Lessig that his retail prices were so high that a loss df sales and customers was likely.” T[iis was one of several instructions which isolated particular incidents from the total course of Tidewater’s conduct and pronounced each lawful. These instructions were no doubt accurate, so far as they went. However, as the Supreme Court recently stated, “[i]n cases such as this, plaintiffs should be given the full benefit of their proof without tightly compartmentalizing the various factual components and wiping the slate clean after scrutiny of each. ‘ * * * [T]he character and effect of a conspiracy [or combination] are not to be judged by dismembering it and viewing its separate parts, but only by looking at it as a whole. * * * ’ ”; and “acts which are in themselves legal lose that character when they become constituent elements of an unlawful scheme.” Continental Ore Co. v. Union Carbide & Carbon Corp., 370 U.S. 690, 699, 707, 82 S.Ct. 1404, 1410, 1415, 8 L.Ed.2d 777 (1962).14
We have said that it would be reversible error to instruct the jury that particular acts, alleged to be part of a conspiracy, were lawful, without adding the express qualification, “in the absence of conspiracy” (Fox West Coast Theatres Corp. v. Paradise Theatre Bldg. Corp., 264 F.2d 602, 606 (9th Cir. 1958)), and it is at least clear that an instruction that a component element of an allegedly illegal course of conduct is lawful should be accompanied by a substance of the admonitions which we have quoted from Continental Ore Co.15
[467]*467D. Alleged error in exclusion of evidence
No substantial error occurred in the exclusion of evidence relating to resale price maintenance. Most of the excluded material was cumulative or only remotely relevant, and the discretion of the trial court in dealing with it was accordingly broad.
II
Exclusive Dealing and Tying Arrangements
Lessig offered evidence of the following circumstances in support of his algation that Tidewater imposed upon its dealers a system of exclusive dealing and . tying arrangements applicable to petroleum products, and to tires, batteries, and automotive accessories (TBA) whi ch Tidewater sold or sponsored.16
Tidewater’s service station(ieájig) were renewable annually, and were subject to cancellation _at six-month intervals on-thirty days’ notice. Each dealer contract ended automatically upon terminar tion of."that dealer’s lease. The dealer was required bv his contract to purch3.se from Tidewater “his total requirements" o‘f gasoline, motor oils and greases, regularly manufactured and sold by” Tidewater, to an amount specified in the contract; and the amount specified in each dealer contract was the estimated full requirements of that dealer’s station. When the servicestation lease and dealer contract were execúted Tidewater’s representatives t.o|d the, dealer that he was to purchase iVom Tidewater his reqfprgrqents of petroleum products and TBA items which it sponsored or sold. Tidewater’s representatives accompanied salesmen of sponsored merchandise while the latter secured orders from dealers. Tidewater’s representatives inspected dealers’ stations for competing merchandise, required that it be returned, and threatened nonrenewal of the offending dealer’s lease. Credit card sales of non-sponsored merchandise were charged back to the dealer if the customer failed to pay. New dealers were required to purchase from outgoing dealers only inventory purchased from Tidewater.
the / i^P The record disclosed the disproportionate' size and economic strength of parties.17 There was evidence that Tidewater imposed exclusive dealing and ty-wishes* to provide Tidewater with noncompetitive acces’s to the portion of the irtarket which the dealers’ stations represented. Dealers testified that they feared to buy competing brands of oil ancH sponsored TBA items even when requested by customers and even though the cost to dealers v/as less, and that when they purchased competing merchandise they hid it.
Evidence was offered that Tidewater — > entered into leases and dealer contracts. containing provisions similar to those described, with about 2,700 service station operators in eight western states. Some of the practices described admitted — ly were followed with respect to all Tidewater dealers, and the others appeared to be of quite general application. Thus, the jury could conclude that the restrictive provisions and practices affected a substantial portion of Tidewater’s sales') to its dealers of about 310 million gallons ( of gasoline annually (about five per cent of the gasoline sPld through dealers in the area), and four to five million dollars worth of TBA.
From this evidence the jury could conclude- that Tidewater sold petroleum; products and sponsored TBA to its deal-[468]*468i ers upon conditions and understandings \ —express and tacit, oral and written— that they not deal in commodities sold by [jgpmpetitors of Tidewater. The only ' serious question is whether the jury could falso conclude that these conditions and * ................. ■■■ ■ - - —• understandings might lessen competition substantially or tend to create a monopoly in a line of commerce, as required by [the Clavton Act-
We think Standard18 and Rich-field Oil19 reauire^JiolALur that, the jury cquld so conclude from such relevant, factors, common to those cases and this, as t ? — - ’ the following: the limited number of ["desirable station sites and the substanI tial investment required to acquire and | develop "them ; the Iqjge number of stations to which eorhpetitive access was denied; thedarge volume of gasoline and SiA retailed by those stations, and the istantial share which these sales ren;ented of total sales of gasoline in the stern states; the fact that^the restricf=»tive condition was imposed not only upon \ the sale of Tidewater’s own petroleum | products,, but also upon the sale of TBA Bs produced and sold by others; the parked C (imparity in the bargaining power of the parties; and evidence that the restricy-tive condition was imposed for the very \ purpose or eliminating competition for 1 dealer patronage.
As Tidewater points out, the percentage of service stations in thlT market affected bv its conduct was not establishetrin the pT~Qs°nt as it was Sta^~ard. However, the percentage of sales of gasoline in the - area made through Tidewater stations was shown (about 5-per cent as .compared with. 6.7 per cent in Standard), and- yyouldr-seem to xeflectthe impact of the restrictive arrangements more accurately than would the percentage of retail outlets affected.20
Tidewater also points out that the record did not disclose total sales m themwestem states of any of thé TEA items involved, and hence the share sold through its stations could not be deter-' mined. In^Standard such information! was available as to some TBA items. 1 However, knowledge .of the share of the"'' market foreclosed is .not invariably required to determine whether exclusive" dealing arrangements violate Section 3 of the Clayton Act. The test remains, /«whether the jury can find from all the ( circumstances that the effect of the par- \ ticular arrangements “may be to substantially lessen competition or tend to create /a monopoly in any line of commerce11; 7and, as the Clayton Act tying clause cases ^demonstrate, thisjmav appear from facts other than the proportion of total commerce in the relevant market which is subject to restraint,.21 **
In Standard the proportion of ’ total sales of automotive accessories affected was not shown, and the evidence [469]*469was that Standswilg gaUH nf tiras and •hat+PT-iPfi “^STT-o nmmv, eg to oifhpr nf tfiese nrndnets. e.yeeeded 2#. óf the total sales in the Western area” (337 U.S. at 296-297, 69 S.Ct. at 1053-1054, 93 L.Ed. 1371). Clearly, the Court’s conclusion that competition might...he. lessened substantially did not rest, upon the nrooor: tion foreclosed of totafacommerce in these products. The (fprobabik basis for the . Court’s concTusi<mréqualIy applicable to the present case, was that dependence upon Standard- for petroleum supplies and station leases so restricted dealer freedom of choice that arrangements recmirlng dealers to-jnnrchase TBA from Standard, in their anti-competitive effect. “shpgld-perhAps,” as Justice Frankfurter said, “be considered, as a. matter of classification. tving rather t^flh rpfl11,‘T-°ments agreements.” 337 U.S. at 305 n. 8, 69 S.Ct. at 1058, 93 L.Ed. 1371.22
We are also satisfied that ' other grounds of distinction suggested by Tidewater between this case and Standard do not justify a different result.23
As an independent theory of violation, applicable to TBA, Lessig contended thafj Tidewater leased its service stations and sold its petroleum products on the condition that its dealers purchase the TBA which it sponsored or sold.
Of course, if a substantial*^ volume of TBA were involved. Tidewater possessed coercive economic power over its dealers because of its role as a lessor of service stations and distributor 61 petroleum products, such tying arrangements would violate Section 3 of the Clayton Act: they would violate Section-1 of the Sherman Act as well if both-of these conditions were present24 The/ quantum of power over the tying product prerequisite to.Sherman Act violation is' simply ‘‘sufficient economic power to impose an appreciable restraint on free competition in the tied product * * [470]*470Northern Pac. Ry. v. United States, 356 U.S. 1, 11, 78 S.Ct. 514, 521, 2 L.Ed.2d 545 (1958).25 This power “may be inferred from the tying product’s desirability to consumers or from uniqueness in its attributes.” United States v. Loew’s Inc., 371 U.S. 38, 45, 83 S.Ct. 97, 102, 9 L.Ed.2d 11 (1962). For this reason, and because power to monopolize need not be demonstrated, it is “seldom * * * necessary m a tie-in sale case to embark upon a full-scale factual inquiry into the scope of the relevant market for the tying product and into the corollary problem of the seller’s percentage share in that'market.” 371 U.S. at 45 n. 4, 83 S.Ct. at 102, 9 L.Ed.2d 11. Indeed, the requisite control of the tying product may be inferred from the seller’s success in imposing a tying condition upon a~~SUDstantial amount of commerce in the tied product, at, least in the absence of some other explanation for the existence of the restraints.26
In the present case there was evidence from which the jury could infer that the alleged tying arrangements were imposed as a matter of general practice, and therefore affected t.ha — snb&tantial volume of TBA sold by Tidewater’s dealers. The jury could also find that Tidewater possessed the economic power requisite to Sherman Act violation from the fact that it successfully imposed tying conditions upon a substantial volume-of TBA sales, and from the following ci.renmstances. Tidewater could cancel dealer contracts on short notice^ and ae-eline to renew them upon expiration.. The consequences of termination" were-disproportionately grave to the , dealer. Tidewater could substitute one dealer for another readily or onera.te the station tor-itself. The dealer was economically bound to his station and to Tidewater's petroleum products-; they were to him (mimifil The good will of his business attached to them: moreover, he was bound by contract to purchase his requirements of petroleum products from Tidewater; and even if he were free to shift, a change would involve substantial expense,27 and the dealer’s economic resources were usually limited.
We are satisfied that there was sufficient evidence of exclusive dealing and tying arrangements violative of the antitrust laws to go to the jury.
[471]*471B. Sufficiency of evidence of damage
Tidewater argues that even so there was insufficient proof of damage to justify submission to the jury of this phase of Lessig’s case.28
Lessig did not contend that the alleged exclusive dealing and tying' arrangements led to the cancellation of his lease; and we agree with Tidewater that there is little evidence that Lessig was damaged prior to the termination of his leáse by the requirement that he purchase petroleum products exclusively from Tidewater.29 However, there was evidence that the prices which Lessig paid for sponsored TBA during his occupancy of the station were higher than those at which such items were available from other sources. Evidence that a merchant has been required to pay more for goods which he resells is sufficient to establish, prima facie, that he has been damaged;30 tested by common experience, such proof is adequate to “establish with reasonable probability” that profits on resale were less. Flintkote Co. v. Lysfjord, 246 F.2d 368, 392 (9th Cir. 1957).31
Tidewater argues that higher cost of sponsored TBA would not necessarily mean lower dealer profits because competitive TBA might not be equally salable and its purchase, even at lower prices, might lead to diminished profits through fewer sales, lower resale price, and narrowed margins. Under Tidewater’s hypothesis, the only wholly satisfactory evidence of damage would be a record of sales of both competitive and sponsored brands of TBA at Lessig’s service station during the same period, Since, arguendo, Tidewater’s illegal activity made the production of such evidenee impossible by preventing Lessig from dealing in competitive TBA, Tidewater cannot complain that the preferred proof was not produced.32
As to the amount of damage, the evidence showed how much more some items of sponsored TBA cost than com[472]*472petitive brands and the quantity of the former Lessig purchased,33 and there was nothing in the record to support Tidewater’s suggestion that competitive TEA might have been less salable or more costly to sell. This was “relevant data” from which the jury could have made “a just and reasonable estimate” of damage. Bigelow v. RKO Radio Pictures, Inc., 327 U.S. 251, 264, 66 S.Ct. 574, 90 L.Ed. 652 (1946).
Relying upon Standard, Lessig requested the court to instruct the jury that if it found Tidewater’s dealer contracts imposed an exclusive dealing requirement34 with respect to petroleum products, “and -this practice affected a substantial amount of commerce, you should find that defendant has violated the antitrust laws.” The instruction-was properly refused. As Tidewater points out, more appeared in Standard than that •fee offending contracts affected a substantial amount of commerce in petroleum products.
We agree with Lessig, however, that the iurv was not sufficiently advised that illegal tying arrangements might be found in tacit conditions or understandings inferred from all the circumstances of the case. Tidewater points to the use of the adjectives “express or implied” in the pertinent instructions, but an adequate explanation of the concept of tacit conditions or understandings established circumstantially cannot be conveyed by a phrase. The danger of confusion was increased by language repeatedly emphasizing the necessity for an agreement.35
The court’s instructions conditioned recovery unon a finding that Lessig entered into an exclusive dealing or tving arrangement, ydfh Tidewater. , But Lessig’s charge was broader;36 he*also alléged that Tidewater sought to irnnose these arrangements unoi/^al^ its dealers. If Lessig proved damage to himself from such a course of conduct — for example,, by cancellation of his lease and dealer contract because he refused to become-dealing..and tying arrangements — we see-no reason why he could not recover. He clearly could if the arrangements violated the Sherman Act.37 Doubt has been raised that proximate cause can be shown where-^nly-^he^Iavton Act is offended-, but webeíieve the distinction untenable. Lessig’s allegation that Tidewater established a system of restrictive arrangements is essential to his Clayton Act case-because an exclusive dealing and"tying arrangement with Lessig alone could not have had the probable effect upon commerce reouired to make nut a violation. Since it is the entire system of conditions and understandings which violate-the Clayton Act, injury to a dealer resulting from Tidewater’s efforts to estahlish and maintain that system is injury [473]*473“by reason of” conduct forbidden by the Act.38
The court instructed the jury that there was no evidence from which it could find that Tidewater's conduct might “tend to create a monopoly” in TBA, leaving t.n t.bp jury only the question of whether it might “substantially lessen competition.” In the context of this case the distinction is scarcely clear; it was not taken in Standard or Richfield, and we can find no reason to take it here. The Clayton Act’s prohibition of agreements which “tend to create a monopoly” is violated though “the tendency is a creeping one rather than one that proceeds at full gallop; nor does the law await arrival at the goal before condemning the direction of the movement.” International Salt Co. v. United States, 332 U.S. 392, 396, 68 S.Ct. 12, 15, 92 L.Ed. 20 (1947).39
The jury was instructed that Tidewater could “urge and encourage” its dealers to buy "all ffieír TBA” from Tidewater, and “express disappointment” if it found they were buying from others. We think the instruction went too far. If the evidence established that Tidewater followed the course of conduct deseribed and that Tidewater’s dealers thereafter purchased from it their requirements of sponsored TBA items, an inference of tacit agreement would be virtually compelled. The instruction thus might preclude the jury from finding tacit agreement from circumstances which would justify such a finding.40
Lessig’s remaining objections to instructions relating to TBA tying and exclusive dealing arrangements seem to us inconsequential, unlikely to arise again, or clearly without merit.
D. Alleged error in exclusion of evidence
One of Lessig’s contentions concerning the exclusion of evidence relating to this phase of the case merits comment. Lessig complains that he was not permitted to state his opinion as to the profit which he lost as a result of Tidéwáter’s alleged conduct. ' Such opinion testimony is. admissible,41 but only if based upon facts which rationally support it.42 The offer of proof was simply that it was Lessig’s opinion, based upon his experience and knowledge, that but for Tidewater’s restrictive practices his earnings would have approximated seven hundred dollars a month, or about four hundred dollars per month more than [474]*474lie in fact averaged. There was no offer to show how his estimate was made, The testimony was inadmissible, absent this foundation, and it was excluded upon that express ground. . '
jjj
Attempt to Monopolize
We think the court erred in withdrawing from the jury the charge that Tidewater attempted to monopolize in violation of Section 2 of the Sherman Act.
The essence o monopo y is power to control pnces and exclude competítion.43 and what we have said demonstrates that there was evidence that Tidewater possessed the specific intent to acquire and exercise such power with respect to a part of commerce.44
Tidewater argues that attempt to monopolize is established only if there is proof of “dangerous probability of sue-cess, i. e., that if unchecked monopolization will result”; that this requires an evaluation of Tidewater’s power in the relevant market; that .the evidence on this issue was inadequate, and such evidence as there was indicated a lack of any possibility that Tidewater could monopolize the sale of petroleum products or TBA.
We reject the premise that probability of actual monopolization is an essential element of proof of attempt to monopolize.45 Of course, such a probability may be relevant circumstantial evidence of intent, but the specific intent itself is the only evidence of dangerous probability the statute requires — perhaps on the not unreasonable assumption ^ actor is better able than others tQ judge ^ practical possibility of achieving his megai objective.46
When the charge -is attempt (or conspiracy) to monopolize, rather than monopolization, the relevant market is “not in issue.” United States v. E. I. Du Pont & Co., 351 U.S. 377, 395 n. 23, 76 S.Ct. 994, 100 L.Ed. 1264 (1956).47 Section 2 prohibits attempts to monopolize “any part” of commerce, and a dominant position in the business of distributing petroleum products and TBA [475]*475was not necessarily prerequisite to ability to attempt to monopolize an appreciable segment of interstate sales in such products.48 If the jury found that Tidewater intended to fix the price at which 2,700 independent service station operators resold gasoline, and to exclude other suppliers of petroleum products and sponsored TBA items from competing for the patronage of these operators, and .took steps to accomplish that purpose, it could properly conclude that Tidewater attempted to monopolize a part of interstate commerce in violation of Section 2 •of the Sherman Act.49
Reversed and remanded.