Abstract: A method and a plant for recovery of oil spilled on a water surface. A marine vessel including a fore body and aft body and a bulwark is provided with a longitudinally extending edge at the deck from which the deck slopes downwards towards a substantially low bulwark which in operating position is below the water surface, thus leaving one side of the deck open to the sea. The sloping deck, the fore body, aft body and bulwark together form an artificial calm bay into which the oil slick can flow. The waves entering the calm bay break against the sloping deck and force the oil at the top of the waves over the edge and then into the interior of the vessel body, where the oil is settled and separated from the body of the water.