The report gives methods and results of an environmental assessment test program at Houston Lighting and Power's T.H. Wharton Generating Station, Unit 52. The aim of the program was to measure emissions changes resulting from applying NOx controls. Emissions of trace elements, organic materials, sulfur species, SO2, NOx, CO, and particulate matter were measured. These emissions, under normal and controlled (for NOx) operating conditions, were compared. Source operating data were also analyzed so that changes in operating parameters and efficiency could be assessed. Unit 52 is a General Electric MS 7001C simple-cycle, single-shaft, heavy duty gas turbine, rated at 70.8 MW nominal electrical output. This gas turbine may use either natural gas or distillate oil fuels. The test program was conducted using oil fuel. Water injection was used for NOx control.