The classical treatment for sweep efficiency throughout the life of a waterflooding project consists of three different stages. The first of which being the period between the beginning of water injection and breakthrough in nearby producers. The second one, the period between breakthrough and the moment where sweep efficiency reaches 100% (full contact of the pattern surface). And a third one, which comprises de period between the end of stage two and the abandonment of the project, during with the remaining efficiencies (displacement and vertical) continue increasing while sweep, of course, remains constant. This paper aims at capturing the variations, in terms on time, values and calculations, that the sweep efficiency suffers as a consequence of initial free fluid saturations of either gas, water or both. Although the possible combinations of three-phase homogenous free fluid initial conditions are infinite, all of them can be fitted within the following six cases: 1. Water saturation = irreducible Sw & gas saturation = 0. 2. Water saturation > irreducible Sw & gas saturation = 0. 3. Water saturation > inflexion Sw & gas saturation = 0. 4. Water saturation = irreducible Sw & gas saturation > 0. 5. Water saturation > irreducible Sw & gas saturation > 0. 6. Water saturation > inflexion Sw & gas saturation > 0. Being the inflexion water saturation the point beyond which the fractional flow curve switches from concave to convex. This paper presents a consistent way of transforming the usual equations used for calculating areal sweep efficiency and mobility ratio, for each stage. In both cases, it will become clear that the equations commonly presented in waterflooding bibliography are, in fact, particular solutions of the larger family of equations derived in this article.