That's because high petroleum prices (higher, at any rate, than they were a few years ago) depress demand for gasoline and jet fuel and thus the markup over raw material costs that a refiner can capture.
FORBES: Magazine Article
2.
Valero Energy , a refiner that processes lower quality crude oil into products like gasoline and jet fuel.
FORBES: Cheap Oil And 2 Other Investing Themes To Profit From In 2013