Since 1971, four peregrine falcons, Falco peregrinus, coated with an oil‐like contamination, have been received for analysis at Monks Wood Experimental Station. All were from north or west Scotland. The contamination from one bird was examined and found to be a highly weathered oil of recent biological origin. The biochemical evidence did not indicate an unequivocal source for the oil, but was compatible with the hypothesis, for which there is strong circumstantial evidence, of fouling by stomach oil from a fulmar, Fulmarus glacialis. The possible circumstances of the oiling are discussed. Stomach oil production by petrels and albatrosses is unlikely to have evolved solely in response to selection pressure for nest defence. Oiling by fulmars appears to a small, but possibly significant, cause of mortality in coastal peregrines.