Carbonate formations are predominant in the Permian Basin and as such are commonly stimulated with acid. Repeated stimulation is typically required to maintain production over the life of the well, but each successive treatment increases the surface area exposed to the acid. Therefore, subsequent treatments of the same acid volume and strength will tend to spend a shorter distance from the wellbore, and production improvements will be moderate. Increasing acid volumes to overcome this problem is typically uneconomic. Instead, use of weak acid has been shown to improve production in over-stimulated reservoirs, by penetrating more deeply into the formation—beyond the large surface area of already-treated rock—before spending itself. To test this concept, slow-reaction acetic acid was used to stimulate 13 mature San Andres wells that had been acidized several times previously, with ever-diminishing response. Production increases of over more than 100% were achieved in three study areas with minimal change in water cut.