Seven companies have already applied for permits to explore for oil and natural gas along all or part of the Southeast coast. All of them want to look off South Carolina.

They would detonate compressed air guns dragged behind ships, creating a series of seismic blasts to read the "echo" beneath the sea floor. To explore the area off South Carolina alone could cost a company some $4 million or more.

These guys mean business.

That's why two public hearings will be held in Charleston on April 27 by the federal Minerals Management Service. The idea that potential supplies off the coast aren't large enough to interest energy companies doesn't mean nobody wants to test the water. Oil companies don't usually do the early surveys, geophysical exploration companies do. Then they sell the data they find.

Whether the supplies or the onshore infrastructure is large enough to make offshore drilling profitable usually doesn't get decided until after a few test wells have been drilled.

"You wouldn't want to preclude anything until you had a better understanding" of the subsurface geology, said Walt Rosenbusch, vice president of projects and issues with the International Association of Geophysical Contractors.

That's enough to get environmentalists alarmed. The seismic blasts would be the latest in an intensifying din along a coast inhabited by the critically endangered right whale, among other species of concern.

A series of blasts from a single compressed air gun can blank out the calls of whales and other marine mammals over an area bigger than New Mexico, said Michael Jasny, of the environmental advocate Natural Resources Defense Council. The animals call to do everything from navigating to feeding to mating. Studies also have shown commercial fish catches drop 40 percent to 80 percent during seismic exploration, he said.

"There's an environmental impact. There's also an economic impact," he said.

Christopher Clark, director of the Bioacoustics Research Program at Cornell University, has studied the effects of seismic exploration off Alaska and ship sounds off New England. Noise levels in the Atlantic have grown 1,000 times higher in recent years, he said.

"The emphasis has been to look for 'bodies on the beach,' " essentially stranded whales or sea life traumatized by a single event, he said. "The chronic accumulation of all actions, little by little, erodes the health of the ocean. The sound has the potential to impact seals, whales, dolphins and everything else."

The federal "scoping meetings" are two of 13 being held along the Southeast coast to get public comments for an environmental impact statement, a preliminary step to deciding whether mitigation and monitoring will be ordered to take place during the surveys. Federal regulations call for companies to share their findings with Minerals Management Service, which makes no bones about its interest.

"It has been more than 25 years since geological and geophysical studies were conducted off the Atlantic coast. This data will enhance, update and supplement information to support future MMS planning decisions for both renewable and conventional energy development," the minerals service news release said.

The Obama administration in March lifted a long-standing ban on new offshore drilling. The S.C. Legislature last year gave the go-ahead for drilling off the coast. The politically charged issue has South Carolinians divided on whether the potential for new energy reserves and revenue outweighs the risks to an $18 billion tourism industry, fishing and other interests.

Derb Carter, director of the Southern Environmental Law Center, said the seismic blasts would disrupt marine life and that the exploration permits would open the way for drilling. "The risk and impacts of drilling off the South Atlantic coast are too great and conflict with both the environmental conditions and the economy," he said.

S.C. Sen. Paul Campbell, R-Goose Creek, who championed the state bill, said he hasn't seen permanent environmental consequences from seismic work in the Gulf of Mexico. "If it's a temporary consequence, that's one thing we've got to live with," he said.

The elephant in the room is uncertainty over just how much oil or gas might be out there. It's generally accepted that not a whole lot of oil lies off South Carolina. There are two types of natural gas fields, the commercially extracted "drier" fields and frozen methane fields that are found off South Carolina, said Mitchell Colgan, College of Charleston geology professor, who formerly worked in exploration research for Shell Oil Co.

"Nobody knows how to drill for them," he said.

Rosenbusch said new technology could belie the old data surveys that concluded there weren't enough energy reserves off the East Coast to be worth drilling. But Colgan said that would surprise him. The offshore subsurface is similar to the land subsurface and that no significant supplies have been found on land.

"With no (onshore) infrastructure in place, you'd have to have a huge oil find out there" to make it worthwhile, he said. "I don't see it happening here. If Shell Oil says it's interested, I would be very interested."