Laboratory endurance tests were performed on a direct injected, turbocharged, and inter-cooled diesel engine. A 25/75 blend (v/v) of alkali refined sunflower oil with diesel fuel and a 25/75 blend (v/v) of high oleic safflower oil and diesel fuel were tested. For comparison prior to the tests with the experimental fuels, a baseline endurance run with Phillips D2 Reference Fuel was carried out.The major problems experienced while operating on the 25/75 blend of alkali-refined sunflower oil and diesel fuel were premature injection nozzle performance deterioration and heavier carbonaceous buildup in the compression ring grooves and on the piston lands. There was no significant problems with engine operation when using the 25/75 blend of high oleic safflower oil and diesel fuel.Based on the results of this investigation, the 25-75 blend of high oleic safflower oil with diesel fuel is a very promising candidate as an alternate fuel.This investigation provides evidence that chemical differences between the vegetable oils have a very important influence on long term engine performance. In the tested fuel viscosity range it appears that the chemical properties rather than fuel viscosity is the major factor which determines engine performance deterioration while using vegetable oil fuels.