The paper presents a detailed analysis of the issues related to an improvement of the efficiency of energy conversion in SI engines, fueled by low-carbon gaseous fuels. The research was conducted on an engine fueled with natural gas (CNG) and methane/hydrogen blends. The applied gaseous fuels are characterized by a reduced share of carbon, which enables a reduction of the emission of CO2. The object of the research was a 1.6 dm3, 4-cylinder engine originally fitted in Opel Astra F. The engine was equipped with a CNG injection system. The final analysis includes the influence of the ignition advance angle and fuel composition on the engine performance and exhaust gas composition.