Both the oil and gas reserves of Western Canada are log-normally distributed. If the total reserves are separated into groups made up of single types of occurrence, these all display log-normal distributions as well. The parameters of the distributions vary considerably for different groups of genetically related accumulations. Many of the distributions also appear to be heterogeneous, showing distinct bimodality. Several hypotheses can be offered to explain this. For instance, the reserves of the group of smaller sized pools may be under-estimated for lack of sufficient information; secondly, geologically unlike types of pools may be grouped together. If the former is the case, an estimate can be made of the additional oil and gas in aggregate that may be undeveloped in the smaller under-estimated pools. The degree of bimodality may also indicate the maturity of an exploration play. Other possibilities are also considered. The distribution curves for the total reserves show only a generalized picture and obscure the characteristics of the individual distributions of the several types of oil or gas accumulations.