Much of the world's oil production during the next three decades will come from state-controlled national oil companies (NOCs), according to research by Houston-based Rice University's James A. Baker III Institute for Public Policy. NOCs are now the world's top oil producers, surpassing the international majors, the institute reports.

However, NOCs that sell petroleum products at subsidized prices will be only 35% as technically efficient as privately held comparable firms that have no obligation to sell products at discounted prices, the institute reports.

"On average, government-held firms in general exhibit only 60% to 65% of the efficiency as the privately held international oil majors. This means NOCs might have more difficulty replacing reserves and expanding oil production than the IOCs that were responsible for 40% of the increase in worldwide oil production capacity in the past 30 years."

The report is based on 13 case studies that examined the history and operations of 15 state-owned oil companies in China, Iraq, Kazakhstan, Russia, Iran, Nigeria, India, Indonesia, Malaysia, Saudi Arabia, Norway and Venezuela.