Petrophysical evaluation for shaly formations is more complicated than that for clean formations. Presence of various modes of shales and clays (laminated, structural and dispersed) makes the petrophysical evaluation even much more difficult In this study, the effects of these modes on petrophysical parameters are discussed. Equations of water saturation, permeability and tortuosity, and the influence of other parameters and various properties and conditions on the three parameters, are also discussed. For the Hibernia and Terra Nova reservoirs, offshore of the eastern coast of Canada, the water saturation, permeability and tortuosity are determined and correlated to each other, using multi-log measurements. An increase in the water saturation and/or permeability is correlated to a decrease in the tortuosity. The three parameters ave strongly interrelated to each other and affected by several lithological and physical characteristics.