The paper presents the results of experimental tests of a FIAT MultiJet 1.3 SDE 90 KM engine equipped with the common rail system, running at full load operation at rotational speeds of n= 1000, 1750, 2000, 2500, 3000, 35000, 4000 and 4200 rpm, carried out on a dynamometer stand. During the tests, the engine was supplied with, respectively, diesel oil and rape oil fatty acid methyl esters (FAME) and their mixtures: B20 (80% diesel oil and 20% FAME), B40 (60% diesel oil and 40% FAME), B60 (40% diesel oil and 60% FAME) and B80 (20% diesel oil and 80% FAME). The paper has assessed the effect of the additions of rape oil fatty acid methyl esters to diesel oil on the unit fuel consumption and the emission of harmful exhaust gas components: nitrogen oxides, hydrocarbons, carbon monoxide, particulates and carbon dioxide. The fuel consumption was measured using a AVL 730 Dynamic Fuel Consumption fuel dosimeter. The measurements of the concentrations of the above-mentioned harmful exhaust gas components were done with a MEXA-1600 DEGR analyzer manufactured by Horiba, while particulate emissions were measured with a MEXA-1230PM analyzer by Horiba.