This article presents a theoretical and empirical model to examine competition in physician private practices implementing a conjectural variation framework. Our study uses the 1998 American Medical Association Physician Socioeconomic Monitoring Survey and tests for collusion and market power in physician private practices. The year 1998 is of particular interest due to charges filed in Federal court by The United States Department of Justice (DOJ) against a number of large physician practices, ruling that physicians could no longer engage in joint negotiations. The indictments by the DOJ were based on anecdotal economic and legal observations rather than the result of empirical evidence from accepted econometric modeling. Our model indicates that the behavior of physicians in medical subspecialties and surgical subspecialties is consistent with a non-cooperative Nash equilibrium.