The thing is, Chavez has already re-negotiated his contracts with the international oil companies several times. Each time they have gritted their teeth and accepted it.
This is not the first time. Its just the latest time.
At the beginning the oil companies were offered rather favorable terms because it was heavy oil, and the technology was uncertain. Since then, as the plants and pipelines have been built, he has managed to force through a better cut for Venezuela by pointing out that the uncertainties had been eliminated. He several times has threatened to “nationalize” their share, publicly, and then has privately assured the oil companies that they were safe, please continue to invest. And squeezed a better percentage out of them each time.
And if the uncertainties went the other way Chavez would have renegotiated in favor of the oil companies?