The U.S. EPA was Mandated by the 1977 Clean Air Act Amendments to determine revised HC and CO emission standards for 1983 model year heavy duty engines. These revised emission standards were to be based on a 90% reduction from the average of actually measured emissions from uncontrolled (1969 model year) gasoline-fueled engines. To comply with the provisions of the 1977 CAAA, ECTD began a baseline testing program. Under this program, in-use 1969 model year heavy-duty gasoline fueled engines were procured, brought to manufacturer's specifications, and then were tested for emissions using the transient test procedure and idle test procedure. The text of this report discusses the vehicle/engine selection and procurement efforts, as well as the engine preparation and testing programs. It also includes a presentation and discussion of the 1969 emissions data.