The compound-specific stable carbon isotope (δ¹³C) analysis of organic residues is commonly used in the identification of lipid residues preserved in archaeological cooking vessels. This paper reports on the δ¹³C values for saturated fatty acids from modern freshwater and brackish fish, wild mammals, domesticated animal muscle tissues, and their milk, collected from Finland and the Baltic Sea. Differences are shown to exist in the δ¹³C values of carcass fatty acids of reindeer (Rangifer tarandus), wild forest reindeer (Rangifer tarandus fennicus), and other ruminant animals. Thus, the results reported in this paper show the importance of using modern reference fat data from similar ecological conditions to those of the studied archaeological site. This is especially vital at sites where wild fauna are known to have contributed significantly to human diet. In addition, discussion on problems related to representativeness of modern reference animal tissues for the interpretation of ancient fats is also carried out.