Fatih Birol said that key Middle East and North African producers would be the overwhelming sources of new supply but that there were signs that governments were diverting investment away from oil. 

"So if the investment doesn't come through as much as we expect to see, this may give an additional boost to prices, and according to our analysis, we may see $150 (per barrel) around 2015," Birol said. 

ICE Brent futures rose to $108.78 per barrel by 1231 GMT on Friday. US crude futures were also up at $98.84. 

With strong demand, disappointing numbers from non-OPEC producers and the fragility of the global recovery, Birol said, it was positive that Saudi Arabia was pumping oil at record levels. 

"Putting all these things together ... I think such news — higher production and higher investment — is very much welcome," Birol said. 

"I would expect the positive developments on the production and investment sides will be factored in earlier or later by the marketplace." 

A senior Saudi oil official said recently that the Kingdom produced 10.047 million barrels per day (bpd) of crude oil excluding condensate in November, the highest rate for decades.

The Organization of the Petroleum Exporting Countries (OPEC) meets in Vienna on Dec. 14 to discuss production policy. 

Birol said oil prices were set to remain high for several years, though a global slowdown would ease some of the pressure. 

"If we see a financial crisis, it would put the prices down, but this will not be permanent, but temporary, and when the global economy is back on its feet, we will have higher prices than we have now," he said. 

"Oil is and will be a risk for the global economy if oil prices remain at these levels or higher." 

In the short term, oil markets are fretting that tougher European Union sanctions on Iran, a major producer, could push oil prices higher.

Birol said it was too early to say anything about possible sanctions and their effects. 

"There is nothing concrete," he said.

"We are just following the market and monitoring the developments on the policy side, on the data side and the market side."