In Keystone XL Debate, Obama's Warning on Oil Exports Rings Only Half True

A growing share of those imports are now going to refiners owned or part-owned by foreign suppliers, such as Saudi Arabia's Motiva venture, or Mexican PEMEX's half-owned 327,000-bpd Deer Park plant. Those contracts are likely to be hard to displace, since many such producers want to maintain a geographically diverse slate of customers.

Ultimately the question of exports may come down to a completely unrelated but equally contentious U.S. energy policy. Exporting domestic crude has been banned for four decades, although re-exporting foreign crude is not subject to the ban.

"The ironic argument to Obama's statements is if we licensed exports of (U.S.) light sweet crude it would open up more capacity in the U.S. refining system to use Canadian heavy crude," Guy Caruso, senior advisor to the energy program at Center for Strategic and International Studies.

"If Obama thinks it's important to keep that Canadian crude in the U.S. we should export more light sweet."

(Editing by Jonathan Leff and Alden Bentley)