The performance and exhaust emissions of a direct injection tractor diesel engine were investigated running the engine on vegetable oils pressed from mustard seeds. Two different mustard seed oils (MSOs) were tested.The unesterized MSOs were cleaned by letting them stand and clear. No modifications were made to the turbocharged diesel engine.The engine generated brake torque with MSOs almost equal to that with diesel fuel oil (DFO). Rather similar brake thermal efficiencies were measured with MSOs than with DFO. Use of MSOs reduced the exhaust smoke and NOx emissions.Exhaust HC emissions were determined using FT-IR technology. No great differences between the fuels were observed in the HC emissions.