An extensive range of fuels has been evaluated in representative naturally aspirated IDI and DI combustion systems with cylinder sizes of 0.61 and 0.62 litre and rated speeds of 70 and 67 rev/s respectively. Performance, gaseous and particulate emissions and detailed combustion data were obtained, with the objective of correlating combustion and performance parameters with a view towards defining an improved engine-based fuel rating technique.The ASTM D613 procedure was found to not accurately predict the ignition delay for vegetable oil and volatile blends of naphtha and methanol with D2. Petroleum and synthetic derived middle distillates and a vegetable oil ester were ranked correctly.Ignition delay was found to feature in defining cold start, noise and light load HC and CO emissions. A relatively simple rating method measuring ignition delay to rank these parameters is discussed, together with the use of heat release for NOx ranking. Several reasons are given illustrating why an overall rating method will be very complex and perhaps not possible. Recommendations are made to highlight the requirements for improvements in fuel rating methods.