The flame/stretch interactions of laminar and turbulent premixed flames are considered both experimentally and computationally. Potentially strong effects of flame/stretch interactions due to preferential-diffusion phenomena within practical turbulent premixed flames were suggested by experiments and numerical simulations of spherical outwardly propagating laminar premixed flames. These considerations were limited to conditions where ignition disturbances, pressure variations, intrinsic unsteadiness of propagating spherical flames, and radiative heat losses were small. Flame reactants consisting of H 2 /O 2 /N 2 and several light hydrocarbon/air mixtures were studied for various fuel-equivalence ratios and pressures of 0.5-4.0 atm at normal temperature (298±3K). The measurements and predictions yielded several interesting results, as follows: Flame response to stretch was linear using a local conditions hypothesis to define characteristic flame length and time scales, yielding constant Markstein numbers f...