Shallow oval bowls used on the Baltic coast in the Mesolithic have been suggested as oil lamps, burning animal fat. Here researchers confirm the use of four coastal examples as lamps burning blubber—the fat of marine animals, while an inland example burned fat from terrestrial mammals or freshwater aquatics—perhaps eels. The authors use a combination of lipid biomarker and bulk and single-compound carbon isotope analysis to indicate the origin of the residues in these vessels.