Seven of 9 oils for this study have experienced varying degrees of alteration. As a result, whole oil gas chromatography and other conventional analyses show little resemblance in composition. Gas chromatography-mass spectrometric analysis of sterane and terpane components of the oil and rock samples permitted the determination of genetic relationship among the rocks and oils.

The North Slope oils can be divided into three groups by the sterane compositions and the sterane and terpane distribution patterns. Group 1 oils, which are least mature and generally referred to as Simpson-Umiat type (Magoon and Claypool, 1981) probably originated from the Lower Cretaceous pebble shale unit. Group 2 oils, reservoired in a wide range of geological formations ranging from Permo-Triassic to Cretaceous, were derived from either the Kingak Shale, the Shublik Formation, or possibly the Sadlerochit Group. Group 3, the most mature oil type, was probably sourced from the deeper Lisburne Group, from which no rock sample was included in this study.