Combustion of propane-air and methane-air in a constant volume spherical vessel are studied. Correlations for the laminar burning velocities of propane-air and methane-air are proposed as a function of initial temperature, pressure, equivalence ratio and diluent ratio. Influences of pressure, temperature, equivalence ratio and diluent ratio over the laminar burning velocity have been studied. During combustion transient pressure rise, gas temperature rise, burnt gas radius, burning velocity etc. are computed at different initial pressure, temperature and mixture composition. The results obtained computationally are compared with experimentally obtained results and also with the observations of other prime investigators. The agreements among different values are, in general, good and within reasonable limits. This also shows the strength and correctness of the proposed correlations.