Evening primrose (Oenothera biennis L.) is a wild species native to Eastern-North America that has recently come under cultivation as an oilseed. The oil is primarily used as a treatment for skin disorders. As a starting point for genetic improvement and domestication of this species, it was thought essential to first characterize genetic variability in Ontario evening primrose, so that members of this population may be drawn upon as a resource during cultivar development. Thirty-six wild evening primrose biotypes were evaluated in replicated trials conducted at the Delhi Research Station during 1988–1990. Seed yield, oil content and the concentration of individual fatty acids were measured. Heritability estimates demonstrated the presence of heritable genetic variation for all characters measured except the C16:1 (n–9) fatty acid. Selection for yield, oil content or fatty acid composition amongst the wild bio-types should therefore be effective. Key words: Oenothera biennis, gamma-linolenic acid, GLA, oil, fatty acid composition