Oil mixed with water from an oil spill along the Yellowstone River is pictured in Laurel, Montana, July 6, 2011. REUTERS/John Warner

A view of the swollen Yellowstone River two miles down stream from the site of the oil spill in Laurel, Montana, July 5, 2011. REUTERS/John Warner

Paddy Cosgrave, co-founder of Web Summit, poses for a portrait after an interview with Reuters in Lisbon, Portugal, September 21, 2016. REUTERS/Rafael Marchante

Paddy Cosgrave, co-founder of Web Summit, poses for a portrait after an interview with Reuters in Lisbon, Portugal, September 21, 2016. REUTERS/Rafael Marchante

The logo of Exxon Mobil Corporation is shown on a monitor above the floor of the New York Stock Exchange in New York, New York, U.S. December 30, 2015. REUTERS/Lucas Jackson/File Photo

Japanese Prime Minister Shinzo Abe addresses the 71st United Nations General Assembly in Manhattan, New York, U.S. September 21, 2016. REUTERS/Carlo Allegri

U.S. President Barack Obama holds up a copy of the Colombian peace agreement given to him by Colombian President Juan Manual Santos during their meeting in New York September 21, 2016. REUTERS/Kevin Lamarque

U.S. President Barack Obama shakes hands with Colombian President Juan Manual Santos during their meeting in New York September 21, 2016. REUTERS/Kevin Lamarque