The paper describes the results of a comprehensive campaign to evaluate the applicability of horizontal wells in the concession area of Petroleum Development Oman. Thirty- one horizontal wells have been completed by June 1991 in ten different fields, covering a variety of reservoir conditions. Test wells have covered both clastics and carbonates, thin and thick oil columns, heavy and light oils, high and low watercuts. Productivities vary from mediocre to spectacular, sometimes with wells only a couple of hundred meters apart. The pace of learning has been rapid and conclusions in general very positive.