In this paper, analysis of the mechanical and environmental performances of a compression ignition engine working with diesel and diesel-biogas as fuels is carried out. The engine has been coupled to an electricity generator and tested at a constant speed of 1800 rpm for different loads. The biogas has been simulated from a mixture of methane and carbon dioxide with a fraction of 60% and 40% by volume, respectively. Decreases of the thermal effi ciency as well as important increases in methane and carbon monoxide emissions in dual-fuel operation were found when the quantity of pilot fuel was reduced. Opacity varied slightly in dual-fuel operation. However, opacity presented a hard reduction in dual fuel operation with respect to diesel operation. Results validate the importance of using biogas as an alternative for Clean Development Mechanisms and a way to reduce economic fossil fuel dependency.