Six leading oil and gas companies have called on governments to enact a carbon-pricing system, saying this would be the most effective way to cut greenhouse gas emissions. The chief executives of Total, Statoil, Royal Dutch Shell, BG Group, BP, and Eni, in a joint letter to the head of the UN Framework Convention on Climate Change, said that governments should use regulatory measures to discourage carbon-intensive energy options and to level the playing field for all energy sources, both renewables and fossil fuels. The executives said the companies are willing to do their part, but that governments need to provide a clear, stable, and long-term policy framework. Total chief Patrick Pouyanne said in a news conference that a carbon price of roughly $40 per ton is needed to spur the replacement of coal-fired power stations, which produce twice as much CO2 as those that use natural gas. And a price of $80 to $100 per ton, he said, would justify investing in carbon capture and storage systems.