Diversion methods are routinely used in both matrix acidizing and fracturing stimulation treatments. In this study, we focus on one of the classical mechanical diversion methods, ball sealers. Ball sealer diversion is used in cased and perforated wells to divert stimulation fluids by temporarily blocking perforation holes in the casing with rubber-coated balls. This diversion method can be very effective, but there is no general methodology to design ball sealer diversion, or to evaluate its effectiveness from the treating rate and pressure record. Experimental data from an extensive series of full-scale flow experiments conducted by BP were analyzed. One field treatment was analyzed and compared, and a similar trend in seating efficiency was observed. Then, we developed an empirical correlation on the basis of BP experimental data. The correlation enables us to estimate how many ball sealers seat on the perforations. By incorporating this correlation into an acid placement model, we can estimate wormhole penetrations along the wellbore with time. We developed a computer program and studied one hypothetical case to show the usefulness of the ball sealer diversion model.