Might cost you more in gearboxes and brake pads though.
Use an appropriate gear to the situation wherever possible -- because it is safer.
Having said that, the best way to get good fuel economy is to keep the car at optimum revs for than engine while accelerating -- if your car puts fuel into the engine while it's decelerating then it's old enough that using it is better for the environment than buying a new one anyhow.
Still, changing from3rd to gth, or other two-gear intervals, should use more fuel than changing properly -- since keeping constant revs is the way to fuel economy.
(you can read more in my book "A fooels gide to economy").
(Me, I'm not... in any way intoxicated, Thu 24 Mar 2011, 18:18, Reply)