Three-dimensional unsteady Navier-Stokes computations have been performed for the ignition and flame propagation above a liquid fuel (propanol) pool in an airflow duct. The article extends the computations of Cai et al. (Combustion Science and Technology, Vol. 174, pp. 5-34, 2002) to include a parameter survey that determines the regimes of pulsating flame spread and uniform flame spread in the initial temperature/opposed air velocity, pool depth, pool width, and oxygen concentration planes. The two flame spread regimes are defined for both earth gravity and microgravity conditions. Pulsating flame spread behavior occurs if the initial liquid temperature and/or the oxygen mass fraction in the incoming airflow is sufficiently low. The roles of surface-tension-driven flow, gas buoyancy, liquid buoyancy, and hot gas expansion are analyzed. The effects of oxygen mass fraction, pool depth, and pool width are evaluated. For narrow pools (2 cm), the three-dimensional effects are focused near the poolside edges where the flame front wraps along the poolside edge but remains nearly two-dimensional over most of the pool. For a wider pool (8 cm), three-dimensional variations in flame shape occur over much of the pool. The behavior of the flame along the poolside edges differs significantly for earth gravity and microgravity conditions. The supply of oxygen due to buoyancy at the edges is an important factor. Contrary to previous speculation, the existence of a "valley'' in the surface temperature pro. le is not necessary to explain the behavior of pulsating spread.