Worked it out once, using a 737-400 as an example (as I had CAP 697 available, and the MRJT example in there is the 734). I seem to remember that at about 2/3 full the aircraft burned as much as a fleet modern, mid-sized car with two to three people per car to carry the same numbers, distance London to Nice as an example. Assuming many of the businessmen would probably drive alone otherwise, over this range the jet is quite an efficient option, certainly the case against air travel is not as clear as environmentalists would say.
For a rough guide a 737-400 uses about 2.5 tonnes per hour of Jet A1 (Sp G around 0.80 kg/litre) and cruises around 430-450 knots TAS.