These files contain data supporting all results reported in Gerdes et al. "Overlooking environmental context causes misidentification of ancient Mediterranean plant oil in organic residues." In the article we found: "Despite the monumental importance of olive oil to the Mediterranean, tracing its early history using archaeological evidence is challenging. Biomolecular methods can recover traces of plant oils from ancient pottery, but similar chemical compositions between plant oils used in the Mediterranean complicate taxonomic differentiation. Moreover, plant oils go rancid easily, degrading into water soluble and volatile products that are easily lost and progressively destroying residues in a buried ancient potsherd. We present experimental evidence of a key additional issue: a calcareous Mediterranean burial environment alters both the amount and composition of olive oil residue preserved in ceramics. We observed both lower yields and a preferential loss of dicarboxylic acid plant oil biomarkers in experimental ceramic samples degraded for one year at 50°C in a calcareous, alkaline soil from Cyprus compared with samples buried in a mildly acidic soil from New York (USA). Our results suggest a need to adapt the biomarker criteria used to recognize plant oil residues to a site’s environmental context in the Mediterranean, where calcareous soils are common. We highlight the impact of our results on efforts to trace the economic importance of plant oils in the Late Bronze Age eastern Mediterranean.