Models of the equation of state (EOS) type, based on the van der Waals (vdW) EOS, are able to deal with phase equilibrium properties of asymmetric systems over wide ranges of pressure, composition, and temperature. EOS type models are of great practical interest. In general, EOSs always give a nonideal behavior for mixtures, regardless the form of the set mixing rules. In other words, EOSs have no access to the "ideal solution" state. However, EOS type models do have access to the "linear system" (LS) state. A LS is a mixture whose EOS parameters depend linearly oil composition. In a LS, the partial molar parameter of a given component within a multicomponent system equals the pure compound parameter. This could be seen as an alternative form of "ideality". In this work, we study the phase equilibria of linear systems. We evaluate the phase behavior of binary linear (and also nonlinear) systems by generating different types of charts including pressure-temperature projections of phase equilibrium univariant lines (PTUL), which are defined by vapor-liquid and liquid-liquid (LL) critical lines, by liquid-liquid-vapor (LLV) lines, and by pure compound vapor-liquid saturation lines. The results of this work are useful to improve our understanding of models of the EOS type.