The existence of major flow systems in the Western Sedimentary Basin of Canada is reflected in the chemical composition and degree of concentration of the formation waters involved. Subsurface salt solution and collapse, and accumulation and destruction of hydrocarbon 'deposits' are directly related to such flow systems. Many occurrences of 'anomalies' in pressure, chemical composition, and concentration may be explained on the basis of membrane behavior of shales. The presence of organic matter may have an important influence on the composition of the formation waters. More sophisticated sampling techniques combined with more detailed analysis of formation waters are needed to develop the full potential benefit of formation-water studies for the petroleum industry.