Exploratory drilling in eastern and northwestern Colorado decreased from 574 wells in 1978 to 427 in 1979. The success rate for exploratory wells increased from 12.5% in 1978 to 20.8% in 1979. Development drilling decreased from 653 wells in 1978 to 594 in 1979. In the Denver basin, 312 exploratory wells were drilled during 1979 with 16.0% success. In northwestern Colorado, 68 exploratory wells were drilled with 47.1% success. Southeastern Colorado had a 14.9% success from 47 exploratory wells drilled. Total drilling in the area decreased from 1,227 wells in 1978 to 1,021 in 1979. The overall success rate increased from 47.5% in 1978 to 51.4% in 1979. Lower Cretaceous Muddy D and J sandstones, Upper Cretaceous Sussex and Shannon sandstones, and Upper Cretaceous Niobrara Chalk were the primary objectives in the Denver basin. Cretaceous and Tertiary units were the main targets in northwestern Colorado, and Paleozoic strata remained the objective in southeastern Colorado.