Three blended fuels with varied levels of tar sands components considered to be representative of future Canadian diesel fuel were tested and compared with a reference fuel in a single cylinder Deutz air-cooled high speed diesel engine. High output tests were performed with 30°C and 5°C combustion and cooling air temperatures. In addition, a rated output test was performed at the 30°C temperature. Engine performance characteristics and combustion parameters were evaluated for all fuels. The effects of the fuels on injection behaviour were also studied.It was found that performance at the test temperatures was acceptable but further evaluation at lower temperatures is required. Slightly advanced injection timing was observed for the denser fuels. Fuels with higher concentrations of aromatics and lower cetane numbers exhibited longer ignition delays, higher cylinder pressures, higher rates of pressure rise and lower thermal efficiencies.