I.e., I see that a semi-trailer/truck can weigh a maximum of 80,000 pounds. How many gallons of cargo (whether it be milk, gasoline, chemicals, etc) does the typical tank trailer hold?
Can be anywhere from 3,500 gal to 9,500 gal. Depending on the density of liquid that is being transported, different number of gallons can be carried to stay under the 80,000 lb limit.