In this work, mathematical models were developed to correlate the brake thermal efficiency, un-burnt hydrocarbons, carbon monoxides and oxides of nitrogen by varying engine parameters like Load and Gaseous (H-2) fuel substitution. The developed models can be used to predict the important performance and emission parameters for diesel-hydrogen operation in various combinations at different loads within the experimental domain. Response surface methodology (RSM) has been applied for developing the models using the techniques of design of experiments and multi linear regression analysis. General factorial design was used to plan the experiments. Second order response surface models were found to be the most suitable in the present work. Analysis of variance (ANOVA) of the experimental results at 95% confidence level revealed that the developed models are significant. Comparison of experimental output with those predicted by the developed models showed close proximity having high correlation coefficients R-2 for the various response variables. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.