A new report by The Guardian reveals ExxonMobil CEO Rex Tillerson, who has been nominated by Donald Trump to be the next secretary of state, is also the head of a joint U.S.-Russian oil company headquartered in the tax haven of the Bahamas. The report is based on documents that were part of the Panama Papers leak. Tillerson is already facing intense scrutiny by both Republican and Democratic lawmakers over his close ties to Russia, which include Exxon’s $500 billion oil deal with the Russian government’s oil company, Rosneft. Considered the largest oil deal in history, the partnership can only go through if the U.S. lifts sanctions against Russia, which the Obama administration imposed over Russia’s intervention in Ukraine.