Economic stimulation of carbonate rocks with acid systems is, one of the most efficient means of increasing production; however, to accomplish success, an understanding of the interaction between proposed acid systems and the formation mineralogy is, paramount, not only from a chemical reaction perspective but also from a physical interaction perspective. Understanding these interactions is of even greater significance with increased reservoir temperatures. Successful stimulation starts with an understanding of the reservoir pore system and composition. An evaluation of fluids to achieve the best differential etching and maintain adequate rock integrity to withstand closure of created conductivity paths is essential to achieving long-term improved production. Obtaining paths of economical penetration is accomplished through the control of both leak-off and reactivity. Case histories covering a wide range of reservoir conditions and geographical areas are presented in which the above mentioned evaluations were implemented to verify or support changes in treatments to improve productivity. Production responses varied from a 20% gain to a 500% gain over other typical treatments in offset wells.