Cnooc Ltd (CEO.NYSE, 0883.HKG) has agreed to form a joint venture with Canada’s Nexen (NYX.NYSE, NYX.TSE) to explore six deepwater wells in the Gulf of Mexico, The Wall Street Journal reported. Cnooc, China largest offshore oil producer, will take a 20% working interest in the Kakuna, Angle Fire and Cypress wells and potentially a 10-25% working interest in three more exploration wells, Nexen said. The agreement is Cnooc’s latest in a string of investments in North America that aim to build up its production and reserves. Nexen, which produces about 20,000 barrels of oil equivalent a day in the Gulf of Mexico, said the agreement is part of its strategy to reduce its interest to a target level of 25-30%. The companies recently formed a partnership to explore the Long Lake oil-sands project in Alberta.