OPEC kingpin Saudi Arabia said that its huge oil reserves - already the second largest in the world behind only Venezuela - are even bigger than previously thought.

The energy ministry said proven oil reserves stood at 263.2 billion barrels at the end of last year, up from the figure of 261 billion barrels that has been used for almost three decades.

The kingdom has another 2.9 billion barrels of crude in a border zone shared with Kuwait, bringing the total oil reserves to 266.1 billion barrels, the ministry said.

Natural gas reserves also grew from 302.3 trillion cubic feet to 324.4 trillion cubic feet, the ministry said.

It said the new figures have been backed by an independent third-party certification by leading consultants DeGolyer and MacNaughton (D&M).

Saudi Arabia is the world’s top oil exporter. It is the third biggest producer after the US and Russia with around 10.6 million barrels per day (bpd).

Energy Minister Khalid al-Falih said Saudi oil remains among the cheapest in the world to extract, at only $4 a barrel.

Meanwhile, al-Falih announced that Saudi Arabia will slash its oil exports in January by 10 per cent compared to November, as producers move to shore up tumbling prices.

Al-Falih said the kingdom would cut its exports to 7.2 million bpd in January, down from 8 million bpd in November. He also announced a further 100,000 bpd cut in February.

OPEC and its allies decided last month to cut their overall output by 1.2 million bpd starting in January, to boost prices hit by a supply glut and fears demand could plummet.

Al-Falih said Saudi production had fallen to 10.2 million bpd, down from the roughly 11 million bpd it was pumping when producers decided to end an output cut deal in May.

After Brent crude hit $85 a barrel in early October, prices dived more than 40 per cent over the next two months due to oversupply and fears of a trade war between the US and China that could slash energy demand.

But prices have partially rebounded in the past few days after a new deal, in which OPEC and non-OPEC producers agreed to trim output by 1.2 million bpd, came into effect in January.