Chevron Corp. (CVX) is doubling down on a big natural-gas bet by expanding its reach into a large swathe of Pennsylvania .

Just three months after completing its acquisition of gas producer Atlas Energy, Chevron is buying drilling and development rights for another 228,000 acres in the Marcellus shale, a rock formation underlying several states in the Northeast that has become one of the most prolific sources of natural gas in the U.S.

While Chevron didn't disclose the price it paid for the additional acreage, analysts estimate that the San Ramon, Calif.-based company paid more than $1.6 billion, based on the amount of gas reserves involved, which are roughly half that of the Atlas Energy deal. In that previous transaction, Chevron paid a little less than $9,000 per acre, according to Argus Research.

Two closely held firms, Chief Oil & Gas and Tug Hill Inc., were the sellers.

"We are taking this step because the price is good and the assets are very complementary with the (Atlas) acquisition we made," Gary Luquette, Chevron's president for North American exploration and production, said in an interview.

So-called shale gas, which is extracted by fracturing the underground rock and then pushing water through cracks to release hydrocarbons, has seen a frenzy of deal making over the past several years. More recently, the world's biggest energy companies have snapped up assets. Exxon Mobil Corp. (XOM) purchased XTO Energy for $25 billion in 2010, and BP PLC (BP) and Royal Dutch Shell PLC (RDSA) have staked out territory in the
U.S.

The rapid emergence of shale gas has sent gas prices plummeting in
North America , which currently doesn't have many facilities to export the gas in liquid form via seaborne shipments. Pressured by prices that average about $4 a million British thermal units, smaller companies are taking advantage of the majors' interest and selling to pay down debt and avoid funding expensive capital expenditures.

For companies like Chevron, low gas prices aren't the only risk. Shale-gas drilling has come under increased scrutiny amid clashes with environmentalists and regulators over the chemicals used in the fracturing process, called "fracking" in industry parlance. Concerns about the safety of drilling activity were heightened last month by two separate accidents in
Pennsylvania . A chemical spill at a Chesapeake Energy Corp. (CHK) natural gas well leaked into a stream and forced the temporary evacuation of families in the area, and a blowout at a gas well owned by closely held CEL Properties forced the evacuation of more than 100 nearby residents.

The purchase of additional acreage shows Chevron's feels "comfortable" with its ability to meet any new regulations aimed at governing natural-gas drilling and protecting drinking-water supplies in the
U.S. , Luquette said.

"Our company has confidence that we can operate with this new heightened expectations from the regulator and the public," Luquette said. "Our internal expectations exceed the regulations of what the state of
Pennsylvania requires."

Pennsylvania 's environmental regulator last month ordered 15 water treatment facilities in the state to comply with tighter regulations and to stop accepting wastewater from drilling operations.

The deal, which is expected to close before the end of the second quarter, is part of a strategy implemented by Chevron last year aimed at acquiring large positions of difficult-to-develop oil-and-gas acreage in early stages of development. The company intends to bring in the latest technology from the
U.S. , the forerunner in shale development, to maximize output.

Over the last year, Chevron has acquired nearly five million net acres of shale gas assets in the
U.S. , Canada , Poland and Romania .

The deal announced Wednesday boosts the company's gas resources, a more liberal indicator of the amount of gas underground than reserves, by 5 trillion cubic feet, roughly the equivalent of more than three months of
U.S. consumption.

Amid a looming shortage of skilled labor in the shale sector, Chevron has made arrangements to retain about 60 employees from Chief Oil & Gas and Tug Hill.

"It's very important that they feel a sense of belonging, and that they don't need to worry about whether they have a job or not," said Luquette, who was flying to
Pennsylvania this week to welcome the workers.

Chevron expects natural gas prices to rebound in the second half of the decade due to rising global demand, he added.

"The question is not if, but when," Luquette said.