If the volume of the population's demand is defined as that quantity of a certain commodity which consumers intend buying in a certain period of time, we may infer that, effectively, the quantities of commodities bought may be smaller than the volume of demand. Of course, such situations occur when supply is lower than demand. Regardless of the duration of such a situation, one may speak of unsatisfied demand. It is therefore of great interest to investigate such demand. As in the case of satisfied demand, the investigations of unsatisfied demand may be carried out by means of econometric or random sampling methods. Whatever the method used, one should bear in mind that the generic designation "unsatisfied demand" refers to at least three particular cases which must be well defined, so that the right method may be chosen and applied.