XTO made several acquisitions last year totaling $4.2 billion including Hunt Petroleum Corp. last year and subsequently saw an output jump of 23 percent to the equivalent of 2.95 billion cubic feet of gas a day. XTO raised its forecast for full-year production growth to 23 percent from an August estimate of 20 percent. Third quarter revenue rose 8 percent to $2.29 billion.

XTO stockholder approval and regulatory clearance, XTO owners will get 0.7098 share of  Exxon for each of their shares, the companies said in a statement. The transaction, the largest energy acquisition since 2006 and Irving-based Exxon’s biggest takeover since the purchase of Mobil Corp. in 1999, values XTO at $51.69 a share, 25 percent higher than its last closing price.

The transaction value includes $10 billion of existing XTO debt and is based on the closing share prices of Exxon Mobil and XTO on Dec. 11.

“We are pleased that Exxon Mobil and XTO have reached this agreement,” said Rex W. Tillerson, chairman and CEO of Irving-based Exxon Mobil Corp.

The purchase is scheduled to close in the second quarter, the companies said.

“XTO is a leading U.S. unconventional natural gas producer, with an outstanding resource base, strong technical expertise and highly skilled employees,” Tillerson said. “XTO’s strengths, together with Exxon Mobil’s advanced R&D and operational capabilities, global scale and financial capacity, should enable development of additional supplies of unconventional oil and gas resources, benefiting consumers both here in the United States and around the world.”

Tillerson said the agreement is good news for the U.S. economy and energy security, as it will enhance opportunities for job creation and investment in the production of America’s own clean-burning natural gas resources.

In a release, XTO chairman and founder Bob R. Simpson said that during the company’s 23-year history, XTO has developed technical expertise and has assembled a substantial, high-quality and diverse resource base in producing basins across the United States, beginning with the Barnett Shale in Fort Worth.

“XTO has a proven ability to profitably and consistently grow production and reserves in unconventional resources,” Simpson said in the release. “As the world’s leading energy company, Exxon Mobil will build on our success and open new opportunities for the development of natural gas and oil resources on a global basis.”

Potential targets include big natural gas companies like Chesapeake Energy, Devon Energy and Anadarko, Gheit said.

XTO shows the priority that major producers are giving to natural gas as a fuel source. New technology has unlocked trillions of cubic feet of natural gas at home, meaning energy producers do not have to navigate tricky political environments overseas.

That doesn’t mean that those projects are being excluded.

Exxon just last week gave the go-ahead for a $15 billion natural gas project in Papua New Guinea, positioning the world’s largest publicly traded oil company to provide energy to a fuel-hungry China.

XTO claims about 45 trillion cubic feet of gas, much of it trapped in tight formations known as shale.

Exxon has signaled recently that it was moving increasingly toward landing natural gas assets. Once the deal closes, Exxon said it will establish a new organization to manage global development and production of unconventional resources.

The company, based in Irving, Texas, will issue 0.7098 common shares for each common share of XTO, representing a 25 percent premium to XTO stockholders. Exxon also will assume $10 billion in XTO debt.

The deal values XTO’s shares at $51.69, based on the closing price Friday.

“XTO has a proven ability to profitably and consistently grow production and reserves in unconventional resources,” Bob Simpson, chairman and founder of XTO, said in a statement.

Simpson is one of the highest paid executives in the United States. His compensation last year was valued at $53.5 million.