Although vegetable oils are apparently an advantageous alternative fuel for direct use in traditional diesel engines with no modification necessary, in practice many problems are regularly discussed in the literature including filter clogging, breakage of certain types of injection pumps, and deposits of carbon on the cold parts of engines. Several technological solutions have been proposed to overcome these problems but the majority of papers discuss them individually and have not actually compared them in similar conditions. The purpose of the present study was to use the same experimental device to compare the three most widely recognised technological options for the use of Jatropha curcas vegetable oil as a fuel in a direct injection diesel engine: preheating, blending with diesel, and recirculating exhaust gases. Power output, specific consumption, thermal efficiency and exhaust gas emissions were compared to those of diesel used as the reference. The results obtained were similar for preheated and non-preheated Jatropha oil, but differed from the results obtained with diesel. Similar combustion performance and similar emissions were obtained with a blend of 20% Jatropha oil and diesel to those obtained with diesel alone. Exhaust gas recirculation (EGR) with Jatropha oil could lead to fouling in the combustion chamber. In contrast to widely accepted theory, this study also clearly demonstrates that the viscosity of vegetable oil is not the main cause of poorer combustion quality and, consequently, of deposits in the combustion chamber.