A study of the motion of the interface in two-phase flow in two dimensions with gravity force parallel to the plane of motion is described. The experiments were run in a porous medium analog, the Hele-Shaw model. A modification of the Saffman-Taylor solution is compared with the experimental results. The arbitrary parameter in the solution, measured in the experiments, does not approach an asymptote but is a function of the ratio of plate spacing to channel height. In the course of the air-water experiments three forms of the interface were observed before turbulence, which indicate regime changes in the flow. Finally, the effects of heterogeneities (change in plate spacing) on the interface were observed.