A computer model for the effusion process commonly utilized in molecular beam epitaxy (MBE) is presented. The model is capable of simulating effusion sources of both conical and cylindrical design. The results of the model, for one MBE setup, shows that the gallium flux incident on a 4×4cm area has greater than a 30% variation and the gallium to arsenic ratio incident upon the same region varies by a factor of 2. A gallium arsenide (GaAs) layer was then grown under approximately the same conditions as used in the simulation. Observation of the layer’s thickness and morphology show reasonable agreement with the computer model’s results.