The negative effect of liquid and gaseous fuel combustion is toxic gases (i.e., carbon and nitrogen oxides NOx) and particulate matter (PM) formation. The content of harmful and toxic components of exhaust gases is strongly dependent on the quality and type of burnt fuel. Experimental research is required to verify the use of current technical and technological solutions for the production of electricity on farms, using various types of conventional fuels and biofuels. The aim of the current research was to comprehensively verify the use of commonly available fuels and biofuels without adapting the internal combustion engine. Gaseous fuels—propane-butane mixture (LPG), compressed natural gas (CNG) and biogas (BG)—were added to liquid fuels—methyl esters of higher fatty acids (RME) and diesel fuel (DF)—in six different power configurations to evaluate the effect on the emission of toxic gases: carbon monoxide (CO), nitric oxide (NO), nitric dioxide (NO2) and particulate matter (PM), and the efficiency of fuel conversion. The use of RME in various configurations with gaseous fuels increased the emission of oxides and reduced the emission of PM. Increasing the share of LPG and CNG significantly increased the level of NO emissions. The use of gaseous fuels reduced the efficiency of the generator, particularly in the case of co-firing with DF. For medium and high loads, the lowest decrease in efficiency was recorded for the RME configuration with BG. Taking into account the compromise between individual emissions and the configuration of RME with BG, the most advantageous approach is to use it in power generators.