Re: fuel cost per passenger ... a fully loaded 747 weighs something in excess of 200,000 lbs. (maybe even 500,000?). Fuel consumption difference from adding another 150 lbs. is minimal.

However, when a plane is fully loaded and trying to determine if has enough fuel to get to the destination, the extra 150-300 pounds of fuel they could carry by leaving behind a passenger can make the difference. This is usually only a factor on older planes, such as 727s, on hot days with heavy headwinds.