Lawmakers of both parties emerged from a two-hour meeting with oil company executives Tuesday saying they are concerned that the Gulf of Mexico oil spill could turn out to be much worse than even the dire predictions they had previously heard.

The oil rig that exploded and sank into the Gulf on April 20 has been widely reported to be leaking as much as 5,000 barrels of crude oil a day, but Rep. Ed Markey (D-Mass.) said officials admitted Tuesday that figure could climb as high as 60,000 barrels a day in the worst-case scenario.

“Every possible human effort must be taken in order to end this threat as soon as possible: That was the message that we were sending here today,” Markey said.

After the briefing with Dave Nagel, executive vice president for BP America, Bob Moran, Halliburton vice president for government affairs, and Greg Panagos, vice president for investor relations and communications at Tranocean Ltd., House lawmakers vowed to press for more information.

They said the executives — joined via telephone by staff on location in the Gulf region — provided unsatisfactory answers about the causes of and response to the incident, particularly about what was being done to stop the leak.

“We asked a lot of questions. We did not get all of the answers that the American people, but especially the people down in the Gulf region, really deserve,” said Markey, chairman of the Energy Independence and Global Warming Committee.

Rep. Joe Barton (R-Texas) described the BP executives as “deer in headlights” and indicated their answers to Member questions were inadequate.

“I think they were trying to be [responsive]. I’m not satisfied with the answers, but I don’t think they were stonewalling the committee,” Barton said.

One of the questions that Markey said lawmakers would probe further is whether there was negligence on BP’s part. “We are not accepting any assurances that we are being given in this meeting as the definitive account of what in fact has occurred,” he said.

Rep. Michael Burgess (R-Texas) agreed that the answers received from executives left something to be desired.

“When you are facing something potentially this massive, I would just think you’d be working lots of different things and not finding excuses [like] ‘We can’t do this’ or ‘We can’t do that.'” Burgess said. “Excuses is probably too strong, but there were explanations that were not satisfying.”

“I don’t know that I got a good answer as far as the burning the petroleum off the surface [of the ocean],” he added. “The weather was cited as a factor, but it’s the Gulf of Mexico — it’s always going to be windy.”

“There should be no limit on what they spend in the short run in order to ensure that this leak is ended and ended as soon as possible,” Markey said, noting that BP recorded a $6 billion profit in the first quarter of 2010. “If this leak is not shut off soon, they will become known as ‘Bayou Polluter.’ And they will be known that way forever. So whatever resources are needed they must put into this effort with money no object.”

Rep. Bart Stupak (D-Mich.), who chairs the Energy and Commerce Subcommittee on Oversight and Investigations, said he was working with Energy and Commerce Chairman Henry Waxman (D-Calif.) to probe the causes of and response to the explosion and subsequent leak.

Stupak said the panels had requested and were reviewing “all kinds of records” from the companies involved and from the Minerals Management Service — which oversees offshore drilling — and that a more formal hearing is planned for May 12 to probe the topic further.

Administration officials also traveled to the Hill on Tuesday to brief Members and staff on the oil spill. Interior Secretary Ken Salazar, Coast Guard Commandant Thad Allen, Commerce Secretary Gary Locke, Environmental Protection Agency Administrator Lisa Jackson and White House energy adviser Carol Browner were expected to brief lawmakers, according to sources familiar with the meeting.

Barton said he hoped the oil spill would not cause Congressional Democrats or the administration to permanently curtail offshore drilling.

“Hopefully this accident is just an isolated accident, and we can find out what caused it and what can be done to prevent it in the future,” Barton said. “What I don’t want to happen is some mass hysteria to take hold and we put a moratorium once again on exploration and a moratorium on new drilling [and] perhaps even a moratorium on existing production.”

Markey and Barton and other lawmakers are planning to travel to the Gulf Coast toward the end of the week to see the spill and its effects firsthand.

Although the spill has sparked renewed debate about the wisdom of President Barack Obama’s plans to expand offshore drilling in certain areas, the focus of Tuesday’s briefing was the short term, with lawmakers pressing company executives to move quickly to shut down the leak.

Key Senate Democrats, meanwhile, acknowledged Tuesday that the Gulf Coast disaster has at least for now set back any efforts to pass legislation to expand drilling.

“I think offshore drilling doesn’t have a very good future,” Commerce, Science and Transportation Chairman Jay Rockefeller (D-W.Va.) said Tuesday.

Rockefeller, whose committee has jurisdiction over drilling safety issues, said he wants to have hearings on the disaster but would likely wait until top Coast Guard and other administration officials are not tied up addressing the oil spill.

Environment and Public Works Chairman Barbara Boxer (D-Calif.) declined to comment on whether the spill would hurt efforts to pass comprehensive energy legislation this year.

But Boxer did note that the disaster is a stark reminder of the need to transition to cleaner forms of energy. “I think it just underscores … the fact that there are so many issues related to drilling offshore for oil,” Boxer said.

Sen. Bob Menendez (D-N.J.) said the oil spill on the Gulf Coast does not have to prevent Congress from finding a bipartisan compromise on climate change legislation, but he suggested Obama should drop his proposal to expand drilling off the coast of United States.

“I don’t think that drilling was the end-all and be-all to a bipartisan effort,” Menendez told reporters Tuesday. He added that the more offshore drilling “may not be the source we need to pursue because of the enormous risk. … There’s a lot of reasons for the president to reconsider.”

John Stanton and Emily Pierce contributed to this report.