A laminar burning velocities database, measured by a shadowgraph method on spherical expanding flames, is still required to improve numerical simulation of kinetic mechanism. Iso-octane/air mixtures at high temperatures (373 and 423 K), high pressure (1, 3, 5, and 10 bar), and high dilution rate were studied over a range of equivalence ratios. CO2, H2O, and exhaust gas recirculation (EGR) were used as diluent over dilution range from 5 to 25 vol%. An explicit correlation giving the laminar burning velocity from the initial pressure, the initial temperature, the dilution rate, and the equivalence ratio is proposed for those flames. Markstein length was also investigated under these conditions. A correlation depending on the same variables was also proposed. Particular attention was given to provide a Markstein length correlation depending on the dilution rate.