bbl = barrel (presumably oil)
mmbtu = million british thermal units (measure of heat)
1 troy ounce = one twelfth of a pound. 1 apothecary ounce = one sixteenth of a pound.
Note to Q.E.D. - I think you meant Avoirdupois. Apothecary weights are another thing, and are based upon Troy weights. In fact, there are only 12 Apothecary ounces in an Apothecary pound (which is the same as a Troy pound).
Also, Troy/Apothecary pounds do not weigh the same as Avoirdupois pounds.
Bet you had no idea you were asking such a complex question, eh Ficer67?