General equations and procedures for using them are presented for multicomponent vapor-liquid-liquid equilibria (VLLE). The Twin Dew-Point Method for binary systems and a Double Rachford-Rice Flash Method for multicomponents are developed leading to simplification of the calculational procedures for many VLLE problems. As an application, new, simpler methods are detailed for solving the phase equilibria in petroleum reservoirs using the Black Oil Model. (c) 2005 Elsevier B.V. All rights reserved.