Leading environmental groups and a U.S. senator called on the government Wednesday to pay closer attention to more than 27,000 abandoned oil and gas wells in the Gulf of Mexico and take action to keep them from leaking even more crude into water already tainted by the massive BP spill.

The calls for action follow an Associated Press investigation that found federal regulators do not typically inspect plugging of these offshore wells or monitor for leaks afterward. Yet tens of thousands of oil and gas wells are improperly plugged on land, and abandoned wells have sometimes leaked offshore too, government regulators concede.

Melanie Duchin, a Greenpeace spokeswoman, said she was "shell-shocked" by the AP report and upset that government wasn't "doing a thing to make sure they weren't leaking."

Of 50,000 wells drilled over the past six decades in the Gulf, 23,500 have been permanently abandoned. Another 3,500 are classified by federal regulators as "temporarily abandoned," some since the 1950s.

Petroleum engineers say that even in properly sealed wells, the cement plugs can fail over the decades and metal casing that lines the wells can rust. Even depleted production wells can repressurize and spill oil if their seatings fail.

Regulators at the Minerals Management Service, recently renamed the Bureau of Ocean Energy Management, Regulation and Enforcement, have routinely been accepting industry reports on well closures without inspecting the work. And no one, in industry or government, has been checking on wells that have been abandoned for years.

The AP found a series of warnings. The General Accountability Office warned in 1994 that leaks from abandoned offshore wells could cause an "environmental disaster." The GAO report suggested MMS set up an inspection program, but the agency never did.

A 2001 study commissioned by MMS said agency officials were "concerned that some abandoned oil wells in the Gulf may be leaking crude oil." But nothing came of that warning.

Regulations for temporarily abandoned wells require oil companies to present plans to reuse or permanently plug such wells within a year - and then an annual review - though the AP found those rules are used to allow wells to remain "temporarily" abandoned forever.

Sen. Mark Udall (D-Colo.) sent a letter yesterday to Interior Secretary Ken Salazar asking whether regulators have authority to inspect abandoned wells. "We can't afford the leak that's now occurring. We certainly couldn't afford additional leaks in the future," Udall said.

Latest videos