The combined effects of hydrogen addition and nitrogen dilution on laminar flame characteristics for iso-octane-air stoichiometric mixtures were investigated. The spherical expanding flames technique, in a constant volume bomb, was employed. The mole fraction of hydrogen in the iso-octane-hydrogen mixture was varied from 0 to 1 and the mole fraction of nitrogen in the total mixture (iso-octane-hydrogen air-diluent) from 0 to 0.4. Measurements were performed at an initial pressure of 0.1 MPa and an initial temperature of 300K. The laminar burning velocity strongly decreases with nitrogen dilution and for all dilution rates increases linearly with hydrogen mass percentage. The burned gas Markstein length is reduced with the increase in hydrogen amount in the mixture until it reaches negative values, the opposite effect of nitrogen dilution. From these new experimental data, an experimental correlation to estimate the laminar burning velocity of iso-octane hydrogen air nitrogen mixtures is proposed. The experimental values of laminar burning velocities are found to be in very good agreement with those predicted by the high temperature mechanism developed by Jerzembeck et al. [1]. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.