A food container made of thin plastic sheet material comprises a bowl and a lid, each having a peripheral sealing region with a downwardly facing channel generally shaped like an inverted “U”. The outward edges of the channels are lockingly engaged. The channels mate and engage to form a primary seal at a conical interface and a secondary seal at a rib. The rib may be on either the base, the lid, or both. Leverage provided by elastic forces in the lid's channel tightens the seals.