With Brent Crude at $115 a barrel, it is little surprise to see the International Energy Agency talking in terms of oil remaining at $100 for 2011. And if it does, the organisation expects OPEC members to generate over $1,000bn in export revenues for the first time, as the FT reported on Wednesday.

Little wonder that Saudi Arabia and the Gulf states, which dominate the 13-nation cartel, can afford to splash out on big public spending plans to help quell social unrest. But it is expensive – Saudi Arabia now needs an oil price of $83 a barrel to balance its 2011 budget. And it may not work: history suggests that as countries grow richer, their citizens want rights as well as rewards.

Political scientists are still refining the theory but they generally accept its central tenets. The development of Europe, east Asia and Latin America has produced many examples of countries where, as incomes have risen, authoritarian regimes have been replaced with more democratic systems.