An individual choosing to drivre a fuel efficient car rather than a guzzler will not appreciably reduce demand.
The demand is really in transportation of goods, not in people who drive to work every day and their car sits there for 8 hours then they drive it home and it sits for another 16 hours with short trips to the store in between.
So you are admitting to contributing to the exportation of unused fuel by both driving a fuel efficient car, and driving less!!! That's Un American when you think about it.