What is the average gas tank size of an 18 wheeler?

between 4.5 and 7.5 mpg. the new engines with the egr systems on them keep drivng the mpg down, bad for the industry. it depends alot on how the driver of the truck drives, keep his foot out of the pedal, of course it'll be higher, also depends on how heavy the load, there are quite a few factors, but 5.5 is average. cost to fill one up, again depends on the fuel tank size and fuel cost, of course, about $3.50 per gal. of diesel fuel most trucks carry about 300 gallons so about $1000 if completely empty. OUCH