A two-dimensional model of the premixed laminar burning of methane-air has been applied successfully to combustion on a slot burner. Computing times could be excessive and a reduced reaction scheme of Peters was found to be satisfactory for nonrich combustion. CARS temperature measurements on such a burner were in good agreement with predictions, as were the flame heights. Heat loss by conduction from the hot gases to the burner surface are shown, both theoretically and experimentally, to be appreciable at low flow rates. Although conditions for flashback could be computed, it was not possible to compute those for liftoff Nevertheless, the conditions that give rise to it can be deduced. The flame curvature and aerodynamic strain contributions to the flame stretch rate provide insights into the liftoff phenomena and these are quantified. Their relationship to local burning velocities enables Markstein lengths also to be quantified for each of the two contributions. As the flow rate increases, negative curvature stretch becomes dominant at the flame tip, whereas at the base of the flame the aerodynamic strain is dominant and negative. The values of Markstein length are such as to induce stability at the tip where the local burning velocity increases with flow rate, and instability at the base where the local burning velocity decreases with flow rate. These effects are reinforced by the diffusion of H 2 toward the tip of the unreacted gases and by heat loss to the burner surface. Consequently, flame liftoff originates at the base.