This investigation concerned the propagation of laminar flame fronts through combustible fuel/air mixing layers above a permeable ground plane. The combustible layers were established by upward diffusion of vapours from a liquid fuel which saturated the permeable ground but did not the ground/air interface. The experiments were carried out using an open trough approximately 240 cm. long, 8 cm. wide, and 25 cm. deep with a smooth ground plane constructed of 100 micrometer glass beads. Ignition, by hot wire, was at one end of the trough, approximately at the stoichiometric mixture level. The fuels were benzene, hexame, heptane, and methyl alcohol. Flame front propagation speeds were determined cinematographically. Total pressure variations prior to, and through the front were measured by a microphone, and the fuel concentration variation above the ground plane were determined by an IR optical scanning system. Propagation velocities of some two to four meters/second were observed, depending upon fuel type and thickness of the combustible zone; no precursor blast waves or detonations were observed. The pressure variations through the propagating flame front were found to have the same magnitude as those of a normal laminar flame. A steady state, quasi-one-dimensional flow theory is presented. Predicted values of propagation velocities were in good agreement with experimental values as a function of fuel type and thickness of the combustible region of the mixing layer.