CLEARFIELD, Pa. - The state's investigation into the cause of a natural gas well blowout in a rural area near here widened Wednesday, when environmental officials suspended a contractor that was working on the well when it went out of control.

The Department of Environmental Protection ordered C.C. Forbes Co., a division of Forbes Energy Services of Alice, Texas, to halt any more well-completion projects in the Marcellus Shale. The DEP ordered the company to hand over equipment records and provide access to employees.

C.C. Forbes was putting finishing touches on the well at the Punxsutawney Hunt Club on June 3 when the well blew out, spewing natural gas, drilling fluids, and saltwater from deep inside the earth into the sky for 16 hours. No one was injured, and the natural gas did not ignite, but state officials say the accident was the most serious incident in the short history of the Marcellus Shale boom.

On Monday, DEP Secretary John Hanger suspended the well's operator, Houston-based EOG Resources Inc.

EOG had hired C.C. Forbes to complete the well - to clean it out and connect it to a pipeline.

"We need to fully investigate the equipment used by this company to ensure that other sites in Pennsylvania are not in danger of experiencing similar blowouts that could place the public or our environment at risk," Hanger said in a statement Wednesday.

"This was a serious incident that could have resulted in the loss of life or significant damage to our natural resources, and the department is prepared to use all means necessary to find the cause of the blowout."

A mechanical device called a blowout preventer failed to stop the eruption.

"At this point, we don't know if it was human error, a mechanical failure, or a combination," said Tom Rathbun, DEP spokesman.

Phone messages left with Forbes in Texas were not returned.

Rathbun said he did not know how many Marcellus wells the contractor had worked on.

Elizabeth M. Ivers, a spokeswoman with EOG Resources, the primary party responsible for the well's development, said the company was constrained to comment while the accident was still under investigation.

"The site and the equipment are in the process of being inspected by EOG and DEP," Ivers said. "We're cooperating fully with the investigation."

DEP officials said the environmental damage caused by the blowout was "modest." A contractor collected 35,000 gallons of fluid that spilled to the ground, most of it contained on the expansive gravel well-pad site, where three other EOG wells are located.

The well had been hydraulically fractured a few days before the completion process began. The process involves the high-pressure injection of water, sand, and chemicals into the shale to release entrapped gas.

Although much of the wastewater was recovered after the fracturing operation, some remained in the ground, and officials say an unknown amount no doubt was included in the mix that gushed out.

Initial news reports quoted State Rep. Bud George, a Clearfield County Democrat who has called for tighter regulation of gas drilling, as saying that as much as 1.5 million gallons of fluid escaped.

In a telephone interview this week, George said that he had gotten the large estimate from a DEP official whose name he did not get.

"Somebody said it. I just don't recall anymore," George said. "The truth of the matter is that when this thing was spewing 65 feet in the air, everybody was excited."