The emission levels that could be reached by development on two combustors representing a 12:1 pressure ratio simple cycle gas turbine, and a 5:1 pressure ratio regenerative cycle gas turbine, both for automotive application were evaluated. Goals were to equal or better the EPA 1975-76 Federal Emission Standards for automobiles. Some 60 atmospheric rig tests were carried out on the simple-cycle combustor whilst 39 atmospheric rig tests were carried out on the regenerative cycle combustor. Some 430 pressure test points involving over 200 modifications to combustor geometry were run. Various fuel injection methods were employed, such as pressure atomizing, air-assisted pressure atomizing and air-blast atomizing. For reasons of reliability and primary zone leanness, the air-blast atomizer was the final selection. The best results were obtained by the introduction of sufficient air to provide a lean head end (in the form of 3 stages of swirl) while maintaining fairly high temperatures in the intermediate zone, the remainder of the air being introduced into the dilution zone. Effects of outside parameters - viz. inlet humidity and regenerator bypass - on combustor emissions were also evaluated.