In the past year, Constellation Power Source Generation (CPSG) has commissioned (or is commissioning) four new combined cycle and simple cycle gas turbine plants. Each of these plants involved different equipment, vendors and architect engineers. Acceptance testing was done for these plants in accordance with ASME PTCs 46 and 22 with support from Fossil Consulting Services, Inc. (FCS). The Performance Test Codes provided the framework for the testing done, but considerable work was required to apply the codes in accordance with relevant contracts. Problems in acceptance testing can result in costly delay and retesting. This paper describes the lessons learned in resolving issues and problems that can help others in planning for and executing similar tests. These lessons learned can also help in writing effective contracts between owners, vendors and architect engineers.