An internal combustion engine system includes a spark-ignited internal combustion engine powered by a gaseous fuel. The engine system also includes an air intake in air providing communication with the internal combustion engine. Further, the engine system includes an exhaust system in exhaust gas receiving communication with the internal combustion engine. The exhaust system includes a methane oxidation catalyst through which at least a portion of the exhaust gas flows and an exhaust gas recirculation line in exhaust gas providing communication with the air intake.