The aim of the study is to obtain an overall assessment of the opportunities and costs for reducing emissions of CO, NOx and "soot" (black carbon - BC). It should also address the potential positive effects of such measures for health, ecosystems and climate from worldwide perspective. This research work was carried out for to control the emissions of regulated pollutants (CO, NOx, and soot) from a light vehicle fuelled with Diesel fuel, unused and waste vegetable oils, and blends of Diesel fuel and oils were measured, as a function of engine speed. Formaldehyde emissions were also quantified, as well as the smoke opacity. The emission levels when using pure or blended oil (25%, 50%, 75%) with diesel fuel are quite similar to the ones from diesel fuel alone, but patterns are found with a small overproduction of CO together with a decrease in NO emissions for the 50% blends. No considerable effect of the nature or previous use of the oil has been found.