This is an interesting just published article relating the costs, challenges and estimate (wild) returns on the two main oil fileds discovery.
Bloomberg.com: Exclusive
Yes, Brazil owns entirely the oil field, like anywhere in the world since the end of colonial times. But Petropras and its foreign partners will receive fantastic fees for pumping out the oil, a financial and technical challenge.
Disclosure: 18-15 years ago, I participated in TV debates, radios, and wrote newspapers articles defending the privatization of Petrobras (I'm still in favour of that) or, at least, the end of its monopoly. Let me add that in that time I wasn't very popular, if anyone knows what was the ideological grounds back then, knows what I mean. But I'm quite glad that at least partnership with international companies are happening. A I hope the government doesn't get to greedy now and try to reverse that. Greedy is a worldwide problem, especially with numbers around trillions.