Outsourcing, etc. can be brought up .
Offshore refinery capacity has been increased & domestic capacity is much more efficient.
Also, reforming technology has made refining as easy as pie.
Look at Valero stock for instance.
Refining may have made improvements, but I don't believe it has very much impact. Just look what happens when single refinery goes offline or has to manufacture designer fuels for Kalifornia or heating oil for the north.
Why has diesel fuel jumped ahead a gasoline prices in the last couple of weeks?