ST. PETERSBURG, June 6 -- The price of oil could surge past $250 per barrel if Western nations succeed in stripping all seven million barrels of Russian daily exports from global markets, Rosneft Chief Executive Igor Sechin warned Saturday at the St. Petersburg International Economic Forum. It was not an appeal for relief. It was arithmetic delivered in the tone of a man who sees the outcome as already determined.

Sechin's calculation rests on what is already happening. Global markets have lost roughly 16 million barrels per day of output because of the ongoing conflict around the Strait of Hormuz, the channel through which one-fifth of the world's crude normally flows. That disruption has driven prices into the $150-to-$160 range. Add R...