This report presents the output of a comprehensive emissions test program designed to measure gaseous Hazardous Air Pollutants (HAPs) from in-production jet engines operating at a range of idle settings and ambient temperatures. The measurement program addressed two primary concerns: total hydrocarbons and speciated hydrocarbons, including HAPs, within the exhaust plume in reasonable proximity of the engine nozzle to capture emissions prior to condensation of volatile gases; and emissions at a downstream location where the plume has cooled to near-ambient temperatures. The measurement program, conducted during three separate campaigns at three different airports, used commercial aircraft equipped with General Electric CFM56 wing-mounted engines to evaluate the effects of change in environmental conditions as well as varying idle speeds. Although the data are attributed to and are defined by this particular engine, additional complementary data have been used to develop an estimation tool using measured data trends as a function of ambient temperature and fuel delivery rates.