Washington, D.C. ? Leading environmental groups and a U.S. senator on Wednesday called on the government 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, state and federal regulators acknowledge.

Melanie Duchin, a spokeswoman with Greenpeace, 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,” but some have been left that way since the 1950s, without the full safeguards of permanent abandonment.