This for sure. Its far easier to rework a refinery designed for heavy, sour oil and make it ready to process light & sweet. And WTI is very light & sweet. More

This for sure. Its far easier to rework a refinery designed for heavy, sour oil and make it ready to process light & sweet. And WTI is very light & sweet. More and more refineries in the US have moved to processing more and more light/sweet crude oil as the level of imports lessened.