An improved acidization method is provided in which an aqueous solution comprising one or more esters or polyesters of lactic acid or of glycerol is placed in a well where the esters or polyesters undergo hydrolysis. The hydrolysis of the esters or polyesters occurs at a slower reaction rate than that of several other known acidization esters, such as diethyleneglycol diformate, at temperatures higher than 60.degree. C. or even higher than 100.degree. C. Thus, the solution may be distributed substantially throughout a region in the well where acidization is required before hydrolysis is completed, despite being exposed to relatively high temperatures.