In a loss-of-coolant accident, the pressure suppression pool of a boiling water reactor swells as a steam/ air mixture is expelled from the drywell into the pool and large gas bubbles are formed beneath the surface. Many tests have been performed to quantify pool swell loads, but analytical methods have been limited in their ability to provide accurate loading estimates. With advancement of numerical methods, it is now feasible to numerically simulate the pool swell process. A finite difference solution algorithm is used to solve the transient incompressible equations for the liquid flow field. Boundary conditions at the fluid/gas interface are determined using a simplified gas flow model. The program is used to simulate several pool swell tests; comparison of the simulation with test data shows good agreement.