1. n. 
The abbreviation for concentration in US oilfield units, pounds per barrel. One lbm/bbl is the equivalent of one pound of additive in 42 US gallons of mud. The "m" is used to denote mass to avoid possible confusion with pounds force (denoted by "lbf"). Sometimes, lbm/bbl is written as ppb, but must not be confused with parts per billion. In SI units, the conversion factor is one pound per barrel equals 2.85 kilograms per cubic meter. For example, 10 lbm/bbl = 28.5 kg/m3.