Comment by Retric

That's not really the case. Per passenger mile commercial aircraft get ~70MPG with longer flights tending to have better fuel economy. The trend is really interesting: http://www.slate.com/content/dam/slate/articles/business/the...

So, they are actually very efficient transportation for long trips. Absolute worst case flying around the world is 24,901 mi which uses the same fuel per person as a 35 MPG car commuting 26 miles each way for one year.

PS: You can double check this by considering ~1/3 of the cost of a seat as being spent on fuel.