We compare four approaches for efficient placement of acid in matrix-acidization treatments: MAPDIR, particulate diverting agents, viscous acids, and foams. For each process, we develop analytical equations for flow into each reservoir interval and resulting skin factor. We consider treatments in reservoirs with two layers of different permeability but the same initial skin factor and with the same permeability but very different skin factor. MAPDIR reduces overall skin factor fastest but at the cost of injection of large volumes of acid into the higher-injectivity layer. Particulate diverting agents and foams can both effectively divert acid to the low-permeability or more-damaged layer but at the cost of lower injection rate. In our study, particulate diverters with the continuous addition of the diverting agent to the acid solution are most efficient. However, quantitative comparisons of foam with the other processes is difficult until more data are available for predicting foam performance in the field. The equations developed here can be applied to a wide variety of other field situations and process parameters.