Venezuela's state oil company PDVSA has said it will stop selling crude to the Big Oil firm following a lawsuit filed against Caracas and getting $12 billion in assets frozen. Exxon says it's due more in compensation following Venezuela's move last year to nationalize foreign oil assets, including Exxon's.

The drive to be an energy superpower "has sometimes manifested itself in unilateral changes to existing contracts with international oil companies or moves to further nationalize their energy industry," Mark Albers, senior vice president for ExxonMobil, said in a speech Tuesday in Houston at the annual international energy conference CERAWeek.

He didn't mention Venezuela, but his talk came the same day as their dispute heightened. Albers was asked about it in a subsequent question-and-answer session.

"Obviously (there are) a number of issues that the courts are going to need to decide so I'm not going to comment on those," he said. "I will say we do remain interested in getting into substantive discussions with the Venezuela government and with PDVSA around the fair market value for the assets that have been expropriated."