Oil is measured at 42 gal/barrel
http://en.wikipedia.org/wiki/Barrel
“Oil has not actually been shipped in barrels [1] since the introduction of oil tankers, but the 42-US-gallon size is still used as a unit for measurement, pricing, and in tax and regulatory codes. Each barrel is refined into about 19.74 US gallons (16.44 imp gal; 74.7 L) of gasoline[2], the rest becoming other products such as jet fuel and heating oil, using fractional distillation.[3]
The current standard volume for barrels for chemicals and food is 55 US gallons (46 imp gal; 208 L).”
I just saw your post; & I checked my figures about Imperial gallons in a drum— you are closer than I was in #23. I was going on memory; where, I guess we always just rounded down & called them “45 gallon drums”. (45.797 gallon drum, just doesn’t roll easily off the tongue.)