Abandoned oil and gas wells lurk in the hard rock beneath the Gulf of Mexico, an environmental minefield that has been ignored for decades, 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."

Regulations for temporarily abandoned wells require oil companies to present plans to reuse or permanently plug such wells within a year, but the AP found that the rule is routinely circumvented, and that 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.

There's ample reason for worry about all permanently and temporarily abandoned wells -- history shows that at least on land, they often leak. Wells are sealed underwater much as they are on land. And wells on land and in water face similar risk of failure. Plus, records reviewed by the AP show that some offshore wells have failed.

Asked in multiple requests over several weeks how often abandoned wells have failed, the U.S. Environmental Protection Agency acknowledged Tuesday -- as this story was being released -- that it has had to deal with leaks at abandoned wells in shallow state waters of Louisiana and Texas. The U.S. Bureau of Ocean Energy Management, Regulation and Enforcement -- which oversees wells in federal waters -- also acknowledged Tuesday that it has dealt with "a few" failed abandoned wells farther out in the Gulf. But the information was released only through the public affairs offices and neither agency provided experts for follow-up.

Experts say abandoned wells can repressurize, much like a dormant volcano can awaken. And years of exposure to sea water and underground pressure can cause cementing and piping to corrode and weaken.(Fox News)