This reduction in p and T causes some of the volatile components to come out of solution (evaporate),causing the liquid volume to shrink.This reduction in volume is expressed by the oil formation volume factor,Bo.Thus, the stock tank oil initially in place is:This reduction in p and T causes some of the volatile components to come out of solution (evaporate), causing the liquid volume to shrink. This reduction in volume is expressed by the oil formation volume factor, Bo. Thus, the stock tank oil initially in place is: