Six fuels were blended to represent current and potential future quality Canadian diesel fuels, as defined by the Canadian General Standards Board. Steady state Caterpillar 3406 engine tests on these fuels showed that engine conditions, such as RFM and torque, have more influence than fuel quality on ignition delay and gaseous emissions. For example, increased cetane from 36 to 43 only slightly reduced nitrogen oxide emissions, while smoke, hydrocarbon and carbon monoxide emissions were unaffected. Ignition-improved and natural fuels of similar cetane and volatility provided equivalent cold starting performance and exhaust emissions. Reduced back-end volatility caused significantly more white smoke, but hydrocarbon and carbon monoxide emissions were only slightly raised. A synthetic fuel essentially gave equivalent performance to a conventional fuel, except for slightly lower nitrogen oxides emissions.