Pattern geometry plays a major role in determining oil recovery during secondary and enhanced oil recovery operations. Although simulation is an important tool for design and evaluation, the first step often involves rough calculations based upon areal sweep efficiencies of displacements in homogeneous, two-dimensional, scaled, physical models. These results are available as a function of the displacement pattern and the mobility ratio, M. The mobility ratio is simply the mobility of the displacing phase over that of the displaced, or resident, phase. Because it is possible to compute sweep efficiency analytically when the displacing and displaced phase have the same mobility, scaled physical model results have been verified for unit mobility ratios.