One guiding beacon for me are oil and especially gas companies that have reserves to grow future production combined with good exploration potential (you need a bit of knowledge to understand the latter) - Petrobras certainly fits the bill. I've only ever heard positive reports about the professionalism at Petrobras and this comes out in the fairly measured press releases from the company - that unfortunately are not matched by the government's officials.

Much of oil exploration runs on gut feel, and my gut feel is that the Santos basin may be one of the last great discoveries of petroleum. May as well own a part of that if you understand the risk.