Spherically expanding flames have been employed to determine the laminar flame speeds of liquefied petroleum gas-air mixtures, diluted or not by the combustion exhaust gas, over equivalence ratios from 0.7 to 1.4. The effect of the stretch imposed at the flame front has been explored experimentally, and Markstein lengths are estimated to characterize the flame stretch. After omitting the stretch effect, one has obtained the unstretched laminar burning velocities of liquefied petroleum gas-air flames with or without diluent. Explicit formulas have been obtained to express the laminar burning velocity dependencies on the equivalence ratio and diluent rate. (c) 2005 Elsevier Ltd. All rights reserved.