Nick Shaxson, the TJN media officer has a new book out 'Poisoned Wells: The Dirty Politics of African Oil'. He's talked about it in the US edition of Harper's magazine. Perhaps the most telling quotes are these:

In America, the idea of "no taxation without representation" underpins democracy and capitalism. But in Angola, rulers tax oil companies, not citizens; so they can be as corrupt as they like, oppress or forget about their subjects, and still wallow in oil money.

and:

People often put the problem like this: oil money would be a blessing but politicians steal it, so people don't see the benefits. But it's much worse: the oil wealth not only doesn't reach ordinary people, but it actively makes them poorer. It took me years to really accept this counter-intuitive idea. But after all I've seen, I have no doubts.

Recommended reading.