More than 27,000 abandoned oil and gas wells lurk in the hard rock beneath the Gulf of Mexico, an environmental minefield that has been ignored for decades. No one - not industry, not government - is checking to see if they are leaking, an Associated Press investigation shows. The oldest of these wells were abandoned in the late 1940s, raising the prospect that many deteriorating sealing jobs are already failing. The AP investigation uncovered particular concern with 3,500 of the neglected wells - those characterized in federal government records as temporarily abandoned." More than 1,000 wells have lingered in that unfinished condition for more than a decade. About three-quarters of temporarily abandoned wells have been left in that status for more than a year, and many since the 1950s and 1960s - even though sealing procedures for temporary abandonment are not as stringent as those for permanent closures. As a forceful reminder of the potential harm, the well beneath BP's Deepwater Horizon rig was being sealed with cement for temporary abandonment when it blew April 20, leading to one of the worst environmental disasters in the nation's history. BP alone has abandoned about 600 wells in the Gulf, according to government data.