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The goal of this project was to demonstrate that a Mack E7G engine operating stoichiometric with Exhaust Gas Recirculation (EGR) and a three-way catalyst can meet the 2010 emission standards for heavy-duty on-highway engines. Results using natural gas and gasoline as the fuel are presented. The Mack E7G is currently a lean burn natural gas fueled engine, which was originally derived from the diesel engine. The calibration of the lean burn engine was modified to operate as a stoichiometric engine. An EGR system and a three-way catalyst were added to the engine. One of the lean burn natural gas ratings for this engine is 242 kW at 1950 rpm and 1424 N-m, at 1250 rpm. This rating was also used for the stoichiometric natural gas engine. Transient emissions and 13-mode steady-state emissions tests were conducted on the engine on natural gas. The engine meets the transient emission standards for 2010 for NOx, NMHC, and CO on natural gas.