"Oil is not a commodity," Ken Silverstein is told by a major player in the energy industry.

"It's a political weapon." That's why his exposé of the oil business doesn't concern itself with global warming, pollution (except in passing) or our dependence on fossil fuels. What he wants to show is the culture that develops when commerce - big commerce - intersects with politics.

Large companies like BP don't always need middlemen. For the most part, they can reach out to the governments of oil-rich countries themselves. For the others, there are the fixers, intermediaries who know the leaders, the government officials, the local customs and so on. The rewards, as you would imagine, are stratospheric. But even more interesting is the ambiguous space they occupy. One fixer escaped prosecution when St Lucia made him their ambassador to UNESCO, giving him diplomatic immunity. A New York oil lobbyist who became America's "de facto ambassador to Kazakhstan" wasn't so lucky. The US government, which he claimed had been fully aware of his actions, prosecuted him anyway.

Silverstein shows how the fixers fit into the overall scheme of things, which includes commodity brokerage firms. Less regulated than most businesses, they can operate on the international stage to an extent others wouldn't dare, and the founder of the company he scrutinises here, one Marc Rich, later turned up on the FBI's Most Wanted list.

A book like this wouldn't be complete without its portraits of oil-rich dictators, like the "fantastically corrupt" Teodorin Obiang of Equatorial Guinea, living a lifestyle that the most decadent of Roman emperors would consider excessive while 80% of his people live in abject poverty. Tony Blair is specifically criticised here, accused of spin-doctoring for oppressive regimes like that of Kazakhstan and charging head-spinning amounts of money for bland, uninformative speeches. Finally, Silverstein stops off in Louisiana, where the dominance of the oil industry has resulted in blossoming careers for lobbyists, weak regulation and a wave of pollution lawsuits.

Legislation has forced the oil industry to become more transparent in recent years. But the essentials, and its umbilical link to the foreign policies of world powers, remains unchanged. A highly professional investigative journalist, as well as a trusted friend of one of the world's top oil fixers, Silverstein seems to have been the right man to coax these figures from the shadowy corners of the oil industry out into the light.