Reuters

Venezuela has long been known to hold some of the world’s biggest deposits of oil sands — thick bituminous resources that require substantial investments and refining methods to develop.

In a new assessment (PDF), government geologists with the United States Geological Survey have provided a dramatic new estimate of how much oil is “technically recoverable” from these oil sands, in an area known as the Orinoco oil belt: 513 billion barrels of heavy oil.

The tally far exceeds previous estimates of around 235 billion barrels, and it represents “the largest accumulation ever assessed” by the U.S.G.S.

The Orinoco is a critical component of Venezuela’s claim to holding the world’s biggest oil reserves, ahead of Saudi Arabia’s 264 billion barrels. But while most of the oil found in the Middle East can be extracted relatively easily through traditional production methods, the Orinoco’s oil sands are tougher to produce.

Saudi officials, meanwhile, claim that their potential resource base far exceeds their official reserves.

Venezuela’s government has outlined grand plans to bring foreign companies, including Chinese and Indian firms, to invest in the region, but it has also been mired in contract disputes with former American partners.

Petroleos de Venezuela, the country’s state-owned company, has estimated that the Orinoco belt held a total resource base of 1.3 trillion barrels of oil, but said only a fraction of that could be produced economically.