Realizing that solar had become essential to oil production, petroleum firms set up their own photovoltaic subsidiaries. Exxon became, in 1973, the first commercial manufacturer of solar panels; the second, a year later, was a joint venture with the oil giant Mobil. (Exxon and Mobil merged in 1999.) The Atlantic Richfield Company (ARCO), another oil colossus, ran the world's biggest solar company until it was acquired by Royal Dutch Shell, the oil and gas multinational. Later the title of world's biggest solar company passed to British Petroleum (now known as BP). By 1980 petroleum firms owned six of the ten biggest U.S. solar firms, representing most of the world's photovoltaic manufacturing capacity.