It's Friday, so we're straying slightly afield from covering cars. In this case, we're turning our green lens toward jetliners to look at fuel economy in the sky.

Anyone who travels on a jet more than once has likely more than doubled their non-flying carbon footprint, and there are unlikely to be electric jets in our lifetimes.

So fuel efficiency takes on great importance in the skies, not only for environmental reasons but because it's a huge expense for airlines over which they have almost no price control.

While new technologies are being launched--including diesel aircraft engines and tests using biofuel in jet engines--the Wall Street Journal reports that Department of Transportation data puts the average mileage for all U.S. airlines at 64 miles per gallon of jet fuel per seat.

For context, that's more efficient than a single driver in the 50-mpg 2010 Toyota Prius hybrid, although with four passengers, the hybrid's per-seat mileage soars to 200 mpg.

Newer aircraft are more efficient than older jets, and single-aisle planes better than twin-aisles, so those airlines with the youngest fleets and those with fewest wide-bodies do best on their overall mileage. The three leaders among airlines serving the U.S. are:

  • Alaska Airlines: 75.9 mpg
  • Jet Blue: 71.7 mpg
  • Continental: 69.6 mpg

While the three airlines with the lowest mileage are:

  • United: 62.9 mpg
  • American: 60.5 mpg
  • Delta:  60.4 mpg

The Journal dives into the factors affecting airline fuel economy in great detail, including distance traveled--the longer the distance, the more fuel weight must be carried--chronic delays on some routes and, of course, load factor, or how many of those seats are filled on each trip.

Travelers who often fly shorter routes will also be familiar with the shift from turbo-prop aircraft to commuter regional jets over the last 10 years.

An airline insider notes that while airlines chalked the transition up to a nicer passenger experience, in reality the lower per-seat fuel costs were the deciding factor.

[Wall Street Journal]