From the article:

Just after Bush's inauguration in 2001, Chavez' congress voted in a new "Law of Hydrocarbons." Henceforth, Exxon, British Petroleum, Shell Oil and Chevron would get to keep 70% of the sales revenues from the crude they sucked out of Venezuela. Not bad, considering the price of oil was rising toward $100 a barrel.

But to the oil companies, which had bitch-slapped Venezeula's prior government into giving them 84% of the sales price, a cut to 70% was "no bueno." Worse, Venezuela had been charging a joke of a royalty – just one percent – on "heavy" crude from the Orinoco Basin. Chavez told Exxon and friends they'd now have to pay 16.6%.