Horizontal open hole wellbores in carbonate formations have become an everyday occurrence to improve production economics. Carbonate formations are typically stimulated by using hydrochloric acid. An acid treatment in the well configuration described provides a significant challenge in diversion to accomplish complete stimulation of the laters. Various techniques have been employed to overcome this problem. These include pre-perforated or slotted liners, specialty treating fluids, solid diverting materials and tools. All have had some successes in various regions of the world. Presented are three case histories in which open hole packers and sliding sleeves have been employed with and without the aid of specialty treating fluids. These cases cover Devonian TVD 3,170 m (10,400 ft), Devonian TVD 2,682 m (8,800 ft) and San Andres TVD 1,737 m (5,700 ft) formations. Details of these treatments, as well as production responses, are discussed.