A generalized quartic equation of state has been developed for nonpolar and polar fluids. The quartic equation of state needs only four fluid properties to predict physical and thermodynamic properties over a wide range of temperatures and pressures. These four properties are critical volume, critical temperature, acentric factor and dipole moment. The new equation of state models the repulsive forces between molecules correctly, unlike the cubic equations of state. One of the four roots obtained by solving the equation of state is always negative, making it possible to identify the remaining three roots like the roots of a cubic equation. The quartic equation of state shows superior performance compared with the Peng-Robinson equation of state.