Exxon Mobil's big threat: a calculator By: CNBC.com News October 20, 2013 at 13:00 PM EDT Global institutions loading up on oil and gas investments have been warned by the OECD that they may need to begin calculating the carbon risk in their assets. Read More >> Related Stocks: BP Plc ADR Chevron Corp ConocoPhillips Exxon Mobil