Quoting PPVRA (Reply 7): or an average stage length of 2.501nm (don't have the units, I presume nm), the average U.S. airlines B763 fuel consumption is 1,568 gallons per hour. Multiply that by the current AvGas prices (no idea how much it is), then calculate 20% lower consumption and you'll get the fuel savings.

From same dataset (DOT) we get that 767300 (I guess that DOT doesn't make difference between regular vs.
ER) has 216 seats on average. It flies 12.2 Block hours per day and it has 2.2 departures per day.
some routes
JFKLON = 3009 nm
LAXLON = 4748 nm
MSP
AMS = 3620 nm
Widepodywing gave us that 20,000lbs difference for longer missions.
Let's simplify and assume that fuel burn difference is 20,000 lbs for average mission =9,072 kg. Density of kerosine is 0.8 kg/l and gallon is 3.785 412 L > fuel consumption difference is in gallons 9,072 /(0.8 *3.785 412)= 2,996.
And if we assume that price of gallon is around $2 then trip cost savings are about $6,000. $12,000 for return trip and 365 return trips pre year $2,190,000
( it is highly unlikely that one plane could do that much flying per year.)
And per oneway seat (if we assume 220 seats) $27.
List price of 767300ER is $133.0 millions and 7878 $148.0 millions.
For me 25% and 20,000lbs means that trip fuel consumption is
60,000 lbs ( 9,000 gallons) for 787 and 80,000 (12,000 gallons) for 767. This sounds low compared to
http://www.startribune.com/535/story/458558.html
A330 which uses 6100 less fuel than DC10 when flying
MSP
AMS.
This means that
DC10 uses 6,100/0.3 = 20,333 gallons per trip and
A330 uses 20,3336,100 = 14,233 gallons per trip
but these are real world numbers and include cargo and baggage and probably
Widepodywing used emptier plane.
According to dot A330 uses 1,871 gallons per hour vs. 767300 uses 1,519. Difference is 11,519/1,871 = 19% (which sounds much) but is same magnitude as 12,000/14,2331 =16%.
So we can conclude that numbers seems to be about correct magnitude and more knowledge people can correct my back in the envelope calculations. It seems that fuel saving from 787 would be even larger when compared to A330.
Rottamo