Dark skies are looming for some of the world's biggest oil companies...

But now, those roles – and power positions – are reversing. In just the past few years, we've seen countries use their oil assets like a baseball bat to cow the traditional majors. Venezuela, Nigeria, and Russia all recently renegotiated oil deals with major oil companies by threat (both subtle and overt). In some cases, assets have simply been "nationalized"... also known as "stealing."

That is a mounting problem for traditional major oil companies. I think the traditional majors are about to be eclipsed by a new hybrid – the state-owned oil company.

Don't get me wrong, some of these companies – like Mexico's PEMEX and Venezuela's PDVSA – are still backward, corrupt, and incompetent. Mexico, for instance, has managed to bungle production at Cantarell, the world's second-largest oilfield. However, a few state-backed companies emerged over the last decade as viable oil companies. The short list is Eni SpA of Italy, Total of France, Petrobras of Brazil, and StatoilHydro of Norway.

The national oil company combines the expertise and financial backing of a traditional major with the influence of a sovereign nation.

That works to the investor's benefit in several ways. First, countries like Nigeria and Venezuela will think twice about outright theft when it comes to the state-backed companies. We saw Bolivia's Evo Morales back down from a threat against Petrobras. I don't think he would have backed down from a traditional major like ConocoPhillips. But the wrath of Brazil's government is another matter entirely.

Second, state-run companies tend to get the best oil exploration rights on their home turf. For example, Brazil's oil ministry just cut several prized blocks adjacent to Petrobras' Tupi discovery out of a recent lease sale. You don't see the U.S. Congress cutting out leases in the Gulf of Mexico and handing them to ExxonMobil, that's for sure.

Third, these companies bring influence that extends far beyond oil and gas deals. That means, unlike independent majors, a state oil company can benefit from national trade negotiations.

Don't get me wrong... several of the "conventional" oil majors are still great investments. S&A Oil Report readers have made more than 50% in Chevron shares in just over a year, and I expect we'll double that in the next two or three. You can still find great values here.

But resource investors are crazy to ignore the likes of Petrobras and a few of the companies I mentioned above. We're up 135% in Petrobras in less than a year. Considering it's the world's finest deepwater oil outfit, the big gains aren't all that surprising.

The next time you're looking to add a Big Oil stock to your portfolio, ask yourself if it has the power of sovereignty on its side. It may mean the difference between 20% gain and 100% gain over the next few years.

Editor's note: Matt Badiali is a regular contributor to DailyWealth, a free investment newsletter focused on the world's best contrarian opportunities. We write with a simple belief in mind: You don't have to take big risks to make big money with your investments.