Before revision:  This curve is given in terms of the optimal stopping boundary of an auxiliary family of perpetual optimal selling problems with regime switching .
After revision:  On the other hand, in presence of a concave running cost function it is optimal to instantaneously deplet the reserve at the time at which the commodity's price exceeds an endogenously determined critical level. In both cases, the threshold triggering the optimal control is given in terms of the optimal stopping boundary of an auxiliary family of perpetual optimal selling problems with regime switching .