The fate of accidently spilled No. 5 fuel oil in a small coastal bay in British Columbia was observed 6 times during 4 yr. The oil's composition was first changed by loss of the lower molecular weight components by evaporation and dissolution. Biodegradation accounted for almost complete removal of n-alkanes in the 1st yr. Pristane and phytane were biodegraded more slowly, but were almost completely gone in 4 yr. The non-n-alkane components in the nC28–30 range seem to be the most resistant to degradation of all the components resolved in the gas chromatograms. The resistance to degradation of these components indicates their potential for long-term studies of oil spills. Key words: petroleum, fate, environment, gas chromatography, n-alkanes, pristane, marine fauna and flora