For quick checks on ignition quality, or for cases where a standard testing engine is not available, predictive equations for cetane number (usually known as cetane indices) in terms of commonly measured physical properties are being used. In this work, the potential of surface tension of the diesel fuels as a predictor of the cetane number has been investigated. Through the use of surface tension (ASTM D 971-82), boiling range, and density of 121 diesel fuels with a wide range of cetane number and physical properties, a predictive expression for cetane number has been developed. This expression provides substantial improvements over the most widely used cetane indices. Especially, for the secondary reference fuels T-18 and U-11, the proposed equation provides excellent predictions.