Simulation tests were carried out for diesel oil (ON) and fatty acid Me esters obtained from used cooking oil. The calcs. were based on thermal NO formation according to the Zeldovich mechanism for diesel engines. Reaction rate coeffs. detd. by Baulch, GRI-MECH 3.0 (G) and Heywood were used. The NO concn. calcd. by method (G) was closest to the results of the exptl. detd. NO concn. and was the best method to demonstrate the actual NO concs. formed in an internal combustion engine fueled with alternative fuel and other higher generations fuels with similar phys. and chem. properties.