The increasing concern regarding diesel vehicle emissions and the rising cost of liquid diesel, leads to the need for alternative fuel. Therefore, the option of using conventional diesel engines (with appropriate modifications) as ‘dual fuel engines’; in which gaseous fuels as a supplement for the conventional diesel fuel can be used; is being pursued. When considering a gaseous fuel for use in existing diesel engines, a number of issues are important. These issues include the gas composition supplied to the engine as well as operating and design parameters. For these engines, gas interchangeability is of great significance as fuel gas composition varies from source to source. While studying the interchangeability aspect, it is necessary to formulate the relations in terms of working parameters to predict the performance of the engine. In this work, the Power Performance Prediction (PPP) Charts are formulated to enable direct prediction of dual fuel engine performance with respect to the fuel-air equivalence ratio and diesel substitution limits over the operation load range. Experiments are carried out to validate the assumptions and find out deviation of the proposed theoretical PPP charts from the practical data. The experiments are used to identify the range in which PPP charts predict the performance reasonably well. For this range of load, the practical and predicted fuel-air equivalence ratios are compared. These PPP charts are a useful tool for primary estimation of the operating range of the stationary engines during dual fuel mode with any gas as main fuel.