A thorough investigation of triethylene glycol (TEG) containing systems has been performed. The introduction of a new six-site association scheme for the TEG molecule has shown to be advantageous. Glycols are often modeled using a four-site scheme (abbreviated as 4C) hence ignoring the internal lone pairs of oxygen. The new association scheme also takes these sites into account. The new parameters of TEG are based on the vapor pressure data, liquid density data, and liquid-liquid equilibria (LLE) data (n-heptane), and they are tested for binary systems (methane, n-octane, n-nonane, n-decane, benzene, toluene, ethylbenzene, and water) and different types of phase equilibria (vapor-liquid equilibria (VLE) and LLE) and thermodynamic properties (heat of mixing, activity coefficients). A less extensive investigation has also been performed on tetraethylene glycol (TeEG) containing systems. Similarly, a new seven-site association scheme for the TeEG molecule has been investigated. The new parameters of TeEG are based on vapor pressure data, liquid density data, and LLE data (n-heptane). The performance is similar to that the 4C scheme.