We have spent billions upgrading and expanding our existing refineries. Combined with our falling demand, our refinery capacity is now noticeably larger than our refined product consumption.
Note: our total petroleum usuage is larger than the above graph, but that includes about 2.2 MMBPD of Natural Gas Liquids like propane, ethane, etc.
Click the graphs for the data links.
With the glut of Natural gas out there shouldn't the price of propane go down?