The article first provides an historical account of antitrust criminal penalties and the development of the Antitrust Guideline. This is followed by an illustration of how the guideline operates in specific cases and an explanation of the logic underlying the Antitrust Guideline which is grounded in the economic theory of "optimal deterrence." The article argues that the legal exposure of firms under the existing Antitrust Guideline, coupled with other legal and marketplace sanctions, is likely to be so large that it will cause a serious overdeterrence problem. This will result in substantial costs due to reduced corporate efficiency. Currently, there is insufficient data to confirm or refute the Antitrust Guideline's 10-percent-volume-of-commerce benchmark for markups or the implied 10-percent probability of detection. The available evidence and economic analysis, however, suggests that the 10-percent-volume-of-commerce benchmark is probably much too high for most price-fixing cases that involve substantial volume of commerce and that the 10-percent-volume-of-commerce benchmark may be too small for some bid-rigging cases. Also, the probability of detection for corporate crimes is probably substantially above 10 percent, and other factors such as the significant marketplace penalty imposed on corporate antitrust offenders and the significant increase in sanctions against individual offenders have not been fully considered in the determination of the appropriate organizational sanction. 1 table, appended Antitrust Guideline, and 122 footnotes