The present study reports the effect of hydrogen addition on combustion characteristics of LPG air mixtures for different mixture compositions, temperatures and pressures. Numerical simulation has been carried out using USC Mech II reaction mechanism, consisting of 111 species and 784 reactions. It is found that, variation of the flame speeds were relatively small for various compositions of LPG air mixtures used. Thus 50% propane 50% butane mixture is considered for the present work. The effect of volumetric H-2 addition on laminar flame speed and ignition delay of selected LPG (50% propane + 50% butane) air mixtures is then studied for hydrogen addition ratio varying from 0 < R-H < 0.5 and over a wide range of mixture equivalence ratio. Also, the investigation is carried out for mixture temperature up to 450 K and pressure ranging from 1 to 10 bar. A parabolic variation of laminar flame speed is observed with equivalence ratios giving peak value for slightly rich mixture. A linear correlation has been observed for the flame speed as a function of hydrogen addition, R-H at all the conditions studied. Whereas, power law correlation has been proposed for the hydrogen added LPG air mixture, to understand the dependency of laminar flame speed on temperature and pressure. A generic correlation has been proposed to study the combined effect of temperature and pressure on laminar flame speed. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.