BEIJING (AP) â¿¿ Italian oil producer ENI says it has sold a 20 percent stake in a gas field in Mozambique in southern Africa to China's biggest state-owned energy company for $4.2 billion. The sale announced Thursday to PetroChina Ltd. adds to a string of foreign acquisitions by Chinese mining and energy companies as they try to become global competitors. ENI said it will retain 50 percent of the Area 4 field while three other partners each will own 10 percent. The Italian company said it also signed an agreement with PetroChina, a unit of China National Petroleum Corp., to cooperate in developing a shale gas block in southwestern China. China's state-owned energy companies, flush with cash from the country's economic boom, are spending billions to acquire assets abroad in hopes of profiting from future demand. Some of the acquisitions are aimed at acquiring oil and gas to import to China, the world's biggest energy consumer. But companies also are investing in assets in Africa and Latin America that supply North American and European markets. ENI has described Area 4 in Mozambique as one of the biggest gas discoveries of the past decade. In December, PetroChina agreed to invest $2.2 billion for a 49.9 percent stake in a Canadian shale gas field being developed by Encana Corp. Last month, another Chinese state-owned oil producer, CNOOC Ltd., completed a $15.1 billion acquisition of Canadian energy producer Nexen. It was Canada's biggest overseas energy deal to date. Calgary-based Nexen also operates in western Canada, the North Sea, Africa and the Middle East.