Grain measures. The bushel as it is used by farmers in the U.S. is actually a measure of mass which varies for different commodities. Canada uses the same bushel masses for most commodities, but not for oats.
There is a variety of "barrels" established by law or usage. For example, federal taxes on fermented liquors are based on a barrel of 31 gallons; many state laws fix the "barrel for liquids" at 31 1/2 gallons; one state fixes a 36-gallon barrel for cistern measurement; federal law recognizes a 40-gallon barrel for "proof spirits"; by custom, 42 gallons compose a barrel of crude oil or petroleum products for statistical purposes, and this equivalent is recognized "for liquids" by four states.
