Gasoline
What you failed to note is that only about 70% of the total oil is used in transportation. Not sure how much is used for cars, but after we take out airline, train and trucks, heating oil consumption, and electric generation, it must be at or below 10 million gallons per day for gasoline.
This means that the percentage reduction of gasoline is at least double what you have stated from efficient cars .
30% of the oil is for plastics and other petroleum products. Of course those will go down in a recession.
I do not see the point of including the consumption of the chemical industry in the discussion of vehicle efficiency.
