Exploratory drilling in eastern and northwestern Colorado increased from 423 wells in 1980 to 696 wells in 1981. The success rate for exploratory wells increased from 28.8% in 1980 to 32.5% in 1981. Development drilling increased from 678 wells in 1980 to 885 wells in 1981. In the Denver basin, 527 exploratory wells were drilled during 1981 with a success rate of 31.3%. In northwestern Colorado, 100 exploratory wells were drilled with a success rate of 48.0%, and in southeastern Colorado 69 exploratory wells had an 18.8% success rate. Total drilling in the area was up 44% from 1980 with 1,581 wells drilled in 1981. The overall success rate increased from 40.7% in 1980 to 59.4% in 1981. In the Denver basin, the greatest number of discoveries was made in the Lower Cretaceou Muddy J sandstone. Lower Cretaceous Muddy D sandstone, Upper Cretaceous Sussex sandstone, Codell sandstone, and Niobrara Chalk were also primary objectives. Cretaceous objectives were the primary targets in northwestern Colorado, and Pennsylvanian Morrow sandstones were the primary objectives in southeastern Colorado.