Has US gasoline consumption really fallen by half in the past decade?

Recent blogs have made much of the following chart from the US Energy Information Agency, which shows a rapid decline in gasoline deliveries to retail stations from refiners.

The decline is significant because it reflects gasoline consumption at the retail level. Gas stations don't store large amounts of gasoline on site--they are normally close to running out when they take delivery. So the chart suggests that gasoline usage has fallen by nearly 50% in the past decade.

There is a problem with the data--it seems to be at odds with reality.

There are about 140 million cars on US roads. An average car is driven about 10,000 miles per year. Average mileage is somewhere around 20 miles per gallon. So each car uses 500 gallons per year, or about a gallon and a half each day. That means about 200 million gallons per day across the country. The chart above shows only about 30 million gallons per day being delivered to stations from refiners.

So either some combination of parameters in the above calculation is off by a factor of ten, somebody else is delivering a lot of gasoline to stations, or the data set is incomplete for other reasons. Need more information before we can draw conclusions though.