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 C alk 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.