The company’s proved reserves totalled 24.8 billion barrels of oil and natural gas at the end of 2015, enough to last 16 years. In the past 10 years, it has replaced an average of 115 per cent of the oil and gas it has tapped every year

ExxonMobil failed to replace all of the oil and natural gas it pumped last year with new discoveries and acquisitions for the first time in more than two decades.

The company’s so-called reserve-replacement ratio fell to 67 per cent in 2015, the Irving-based company says in a statement. Prior to that, the world’s largest oil explorer by market value had achieved ratios of 100 per cent or higher for 21 consecutive years.

ExxonMobil held reserves equivalent to 24.8 billion barrels of crude as of December 31, enough to continue current rates of production for 16 years, according to the statement. That is down from 17.4 years or reserves life at the end of 2014, according to data compiled.

The company added reserves last year in Abu Dhabi, Canada, Kazakhstan and Angola. In the US, gas reserves declined by the equivalent of 834 million barrels as tumbling prices for the furnace and power-plant fuel made some fields unprofitable to drill.

The gas reserves removed from ExxonMobil’s books probably will be drilled at some point in the future when prices are higher, according to the statement.

The reserve-replacement ratio is a key measure for oil producers and the investors and analysts who follow them: it’s one indicator of a company’s long-term ability to maintain or expand crude and gas output. The calculation involves adding together all the new reserves acquired, discovered or achieved through technological innovations and dividing that by the amount of oil and gas pumped that year.

2015 reserves additions

Exxon says it added 1 billion barrels of proved oil and gas reserves in 2015, replacing 67 per cent of production, including a 219 per cent replacement ratio for crude oil and other liquids.

At year-end 2015, ExxonMobil›s proved reserves totaled 24.8 billion barrels of oil and natural gas. Liquids represented 59 per cent of proved reserves, up from 54 per cent in 2014. ExxonMobil’s reserves life at current production rates is 16 years.

ExxonMobil replaced only two-thirds of its 2015 oil and gas output

In 2015, reserves were added in Abu Dhabi, Canada, Kazakhstan and Angola. Liquid additions during 2015 totaled 1.9 billion barrels. Natural gas proved reserves were reduced by 834 million oil-equivalent barrels primarily in the US reflecting the change in natural gas prices. The company expects this gas to be developed and booked as proved reserves in the future.

Over the past 10 years, ExxonMobil has replaced 115 per cent of the reserves it produced, including the impact of asset sales.

"ExxonMobil has a successful track record of proved reserves replacement over the long term, demonstrating the strength of our global strategy to identify, evaluate, capture and advance high-quality opportunities," says Rex W Tillerson, chairman and chief executive officer.

"Our proved reserves represent a diverse portfolio that positions us to create shareholder value as we supply long-term energy demand growth. We will continue to apply our disciplined, paced investing approach as we develop our industry-leading resource base."

Reserves additions in 2015 reflect new developments as well as revisions and extensions of existing fields resulting from drilling, studies and analysis of reservoir performance. The annual reporting of proved reserves is the product of the corporation’s long-standing, rigorous process that ensures consistency and management accountability in all reserves bookings. Consistent with SEC requirements, ExxonMobil reports reserves based on the historic average market prices on the first day of each calendar month during the year.

Resource Base

During 2015, ExxonMobil added 1.4 billion barrels of oil and gas to its resource base through by-the-bit exploration discoveries, undeveloped resource additions and strategic acquisitions.

ExxonMobil’s by-the-bit exploration success in 2015 included a significant oil discovery offshore Guyana and additional discoveries in Iraq, Australia, Romania and Nigeria. Strategic unconventional resource additions were made in the Permian Basin in West Texas, Canada and Argentina.

Overall, the corporation’s resource base totaled more than 91 billion barrels at year-end 2015, taking into account field revisions, production and asset sales. The resource base includes proved reserves, plus other discovered resources that are expected to be ultimately recovered.