Abstract: Petroleum values bound in formations by sulfur scale blocked passages are freed by effectively dissolving the scale and formation rock with a solution containing a primary acid, a catalyst, and, preferably, a chelating or sequestering agent and a wetting agent. The primary acid is preferably hydrochloric. The catalyst is tetravalent or pentavalent vanadium. The chelating agent is at least one member selected from the class consisting of dicarboxylic acid, or tricarboxylic acid, or both acids, and glycerine, wherein the above acid group is always present. The primary acid attacks the sulfur scale and formation rock, and its action is substantially completed because of the catalyst. The chelating or sequestering agent maintains the dissolved minerals in solution. The wetting agent enables mineral penetration.