(Nov 7): Oil traded near the highest close in more than two years as political upheaval in Saudi Arabia reverberated through a market already bolstered by signs of tightening supply.

Investors piled into crude as a shake-up of the ruling elite in Saudi Arabia, the world’s biggest exporter, was seen to consolidate power in the hands of Crown Prince Mohammed bin Salman, who supports OPEC-led output cuts. Some also see the purge as raising political instability in the kingdom, adding a risk premium to prices. As OPEC looks likely to extend curbs and U.S. stockpiles shrink, oil remained elevated on Tuesday.

Oil has advanced more than 20 percent since the beginning of September on signs global supplies are tightening and the Organization of Petroleum Exporting Countries and allied producers may prolong their deal to lower output past the end of March. The Saudi purge eliminated potential rivals to the Crown Prince, who has backed extending the supply agreement.

“The fact that the Saudi Crown Prince backs an extension to the oil cuts is one reason why the markets are looking at this as a bullish signal,” said Barnabas Gan, an economist at Oversea-Chinese Banking Corp. in Singapore. “The key factor looking ahead is whether other producing countries take advantage of the higher prices and start pumping more, particularly U.S. shale.”

West Texas Intermediate for December delivery was at $57.22 a barrel on the New York Mercantile Exchange, down 13 cents, at 9:16 a.m. in Hong Kong. Total volume traded was about 57 percent below the 100-day average. Prices rose $1.71, or 3.1 percent, to $57.35 on Monday, the highest close since June 2015.

Brent for January settlement fell 15 cents, or 0.2 percent, to $64.12 a barrel on the London-based ICE Futures Europe exchange. Prices rose 3.5 percent to $64.27 on Monday, the highest close since June 2015. The global benchmark crude traded at a premium of $6.68 to January WTI.

Weekend arrests of princes and officials in Saudi Arabia were “merely the start of a vital process to root out corruption wherever it exists,” the nation’s attorney general said Monday. In the U.S., crude stockpiles probably slid 2.45 million barrels last week, according to a Bloomberg survey before government data Wednesday.