ExxonMobil Corp. last year boosted its global oil and natural gas resource base by 9.8 billion boe through by-the-bit exploration discoveries and strategic acquisitions, the largest gains since acquiring XTO Energy Corp. in 2010, while it added 2.7 billion boe of proved reserves.

The supermajor last year also replaced 183% of production, it said Thursday. At the end of 2017, proved reserves totaled 21.2 billion boe, weighted 57% to liquids from 53% in 2016. Reserve life at current production rates is 14 years.

“Our exploration success and strategic acquisitions made during a period of low commodity prices are adding high-quality resources that are among the lowest cost of supply in the industry,” said CEO Darren W. Woods.

The resource base additions include proved reserves and other discovered resources that are expected to be ultimately recovered. The resource base at the end of 2017 totaled 97 billion boe, taking into account field revisions, production and asset sales.

Additions from liquids-rich unconventional plays in the United States, mainly in the Permian Basin, totaled 800 million boe. Through its $6.6 billion acquisition in early 2017 of entities from the Bass family of Fort Worth, TX, ExxonMobil nearly doubled its Permian resources.

Growth from the Permian is expected to triple by 2025 to more than 600,000 boe/d.

Key resource additions also were made last year in deepwater Brazil pre-salt and onshore Papua New Guinea. Another big addition came in Mozambique with the purchase of a 25% stake in Eni SpA’s Offshore Area 4, the site of the Coral floating liquefied natural gas project.

Proved crude oil additions last year at Upper Zakum in Abu Dhabi totaled more than 800 million bbl. Other new proved reserve additions were made in Guyana, where the first phase of development launched.

Consistent with Securities and Exchange Commission (SEC) requirements, ExxonMobil reports reserves based on the average of the applicable market price prevailing on the first day of each calendar month during the year.

Because of higher commodity prices in 2017 relative to 2016, about 900 million boe in North America qualified as proved reserves under SEC guidelines, primarily because of the extension of the projected economic end-of-field-life.