Almost all U.S. hospitals procure their equipment through group purchasing organizations ("GPOs"). Some hospitals subject the prices secured by GPOs to a second round of competition in an "aftermarket," in which vendors both on and off the GPO contract compete for the hospital's business. To measure the extent of the potential benefit to hospitals from another round of competition, we analyzed a database of approximately 8,100 aftermarket transactions for hospital capital equipment. The transactions data suggest that hospitals were able to achieve average savings of approximately 10 to 14 percent across the entire database (2001 through 2010) and a savings of 15 percent on average for 2010 data. These savings may be attributable to many factors, including the compensation structure of GPOs.