http://www.theglobeandmail.com/report-on-business/china-japan-trade-war-looms/article1722324/

last paragaph

The islands at the centre of the current argument were awarded to Japan by the United States following the Second World War. The dispute over their ownership became far more heated following a 1969 geological survey that indicated that the waters around the islands could be home to as much as seven trillion cubic feet of natural gas and upward of 100 billion barrels of oil.