I was talking with a guy on MSN the other day (he comes on here occasionally) and if I'm remembering correctly, he said he went through something like two gallons of gas in a 2.5mi race, on a new CR125. The same CR125 apparently broke his foot when he tried to kick-start it, in spite of wearing motocross boots. Sounds like a monster.
Anyway, I really can't say what kind of mileage my bikes get, because I really don't know how many miles we actually cover at a time. I do know, however, that my 250 Husky with its 2.1 (or is it 2.2?) gallon tank has about twice the range of Opferman's '83 Maico 490. The 120, with it's ? gallon tank, has quite a lot better range than the 250, though again I don't know what the numbers are. One time, when riding the 120 with my dad's 100 Yamaha (we have a traditional small-bike ride each year) we got way, way, WAY out in the middle of nowhere after getting lost on the way, when the Yamaha ran out of gas going up a hill. It was so underpowered at that time (airbox modification and a longer stinger fixed that) he was full throttle the whole time, so it really sucked it down. He still had reserve, so we limped back to camp. He ran out of gas for real three times more on the way back, and twice we'd take a beer can, fill it with gas from the 120, and put it in his bike. Finally, he gave up and told me to go back to camp. I rode back, put some gas in the 120 (which was understandably almost empty) and then transported a Gatorade bottle of gas to rescue the stranded Yamaha.