U.S. oil major Exxon Mobil Corp has revised down its proved crude reserves by 3.3 billion barrels of oil equivalent as a result of low oil prices throughout 2016, a company filing showed on Wednesday.

The de-booking includes the entire 3.5 billion barrels of bitumen reserves at the Kearl oil sands project in northern Alberta, operated by Imperial Oil, a Calgary-based company in which Exxon has a majority share.

It comes a day after ConocoPhillips Corp de-booked more than a billion barrels of its oil sands bitumen reserves, citing weak global crude prices.

In total Exxon has 20 billion barrels of oil equivalent at year-end 2016, the Securities Exchange Commission filing said. The reduction reflects the number of barrels of oil equivalent that were now deemed uneconomic due to lower crude prices.

In addition to the Kearl volumes, another 800 million barrels of oil equivalent in North America failed to qualify as proved reserves.

However the reductions were partly offset by Exxon adding 1 billion barrels of new oil and gas reserves in the United States, Kazakhstan, Papua New Guinea, Indonesia and Norway.

Under SEC rules Exxon and other U.S.-listed companies report reserves based on the average crude price on the first day of each calendar month during the year.

Benchmark crude prices in 2017 have so far been higher than in 2016, meaning some of the volumes could be rebooked as proved reserves if these levels hold.

Source: www.reuters.com