concurring.
I join in the judgment and opinion of the Court. I do not understand the Court’s opinion to hold that the exchange of specific information among sellers as to prices *339charged to individual customers, pursuant to mutual arrangement, is a per se violation of the Sherman Act.
Absent per se violation, proof is essential that the practice resulted in an unreasonable restraint of trade. There is no single test to determine when the record adequately shows an “unreasonable restraint of trade”; but a practice such as that here involved, which is adopted for the purpose of arriving at a determination of prices to be quoted to individual customers, inevitably suggests the probability that it so materially interfered with the operation of the price mechanism of the marketplace as to bring it within the condemnation of this Court’s decisions. Cf. Sugar Institute v. United States, 297 U. S. 553 (1936); American Column & Lumber Co. v. United States, 257 U. S. 377 (1921).
Theoretical probability, however, is not enough unless we are to regard mere exchange of current price information as so akin to price-fixing by combination or conspiracy as to deserve the per se classification. I am not prepared to do this, nor is it necessary here. In this case, the probability that the exchange of specific price information led to an unlawful effect upon prices is adequately buttressed by evidence in the record. This evidence, although not overwhelming, is sufficient in the special circumstances of this case to show an actual effect on pricing and to compel us to hold that the court below erred in dismissing the Government’s complaint.
In summary, the record shows that the defendants sought and obtained from competitors who were part of the arrangement information about the competitors’ prices to specific customers. “[I]n the majority of instances,” the District Court found, 273 F. Supp. 18, 27, that once a defendant had this information he quoted substantially the same price as the competitor, although a higher or lower price would “occasionally” be quoted. Thus the exchange of prices made it possible for indi*340vidual defendants confidently to name a price equal to that which their competitors were asking. The obvious effect was to “stabilize” prices by joint arrangement — at least to limit any price cuts to the minimum necessary to meet competition. In addition, there was evidence that, in some instances, during periods when various defendants ceased exchanging prices exceptionally sharp and vigorous price reductions resulted.
On this record, taking into account the specially sensitive function of the price term in the antitrust equation, I cannot see that we would be justified in reaching any conclusion other than that defendants’ tacit agreement to exchange information about current prices to specific customers did in fact substantially limit the amount of price competition in the industry. That being so, there is no need to consider the possibility of a per se violation.