Nineteen experimental cooking residues were prepared in replica cooking pots from meat, fish and plants used as food by the Natives of Western Canada. One set of sherds was stored at room temperature for 4 days; a second set was stored under conditions which simulate long term decomposition. The fatty acid composition of the residues were determined using gas chromatography. As a result of thermal and oxidative degradation, the composition of the cooking residues differs from the original foods but distinct patterns of degradation exist. Criteria are proposed for identifying the former contents of vessels on the basis of the relative percentage of medium chain fatty acids, C18:0 and C18:1 isomers in absorbed residues. The discriminatory capability of the criteria is supported by principal component analysis of the highly degraded residues.