Total drilling in the Four Corners-Intermountain area during 1977 increased 84% from 1976. The increase was mostly in development drilling, particularly in the Mesaverde infill drilling in the San Juan basin. Exploratory drilling decreased in southwestern Colorado and western New Mexico, but was up sharply in Utah and Nevada. Exploration in the overthrust belt of Utah was very active with 3 new-field discoveries being made. The Trap Spring oil discovery in Nevada accelerated both exploratory and development drilling in that state. Success rates of 18.9 and 92.3% for exploratory and development wells, respectively, were higher than in 1976. Leasing was heavy in parts of Utah and Nevada and fillings were made on over 4 million acres of state leases in Arizona. Geothermal ex loration continued in western New Mexico and southwestern Utah with an agreement being made to construct a geothermal plant at Roosevelt Hot Springs in Utah. It is anticipated that both exploratory and development activity will remain high and most probably will increase in 1978.