The phase ratio variation PRV method is a classical way to determine the partition coefficients of volatile compounds between their solution and vapour phases in a variety of circumstances. However, some results obtained by this method can be disappointing. A new PRV equation in which the initial liquid-phase solute concentration is replaced by the liquid-phase solute concentration at equilibrium is proposed. This proposed PRV equation is a second-order polynomial equation. To thoroughly examine the possible modes of calculation, noisy dummy data were generated using both the classical, first-order PRV model (PRV1) and the proposed, second-order model (PRV2). Thus, pseudo-data obtained from simulations were compared to published experimental data. We observed that the second-order model, PRV2, produces a lower variability, allowing improved K precision. Moreover, the obtained K(PRV2) values are very close to those obtained by classical equilibrium headspace analysis (EHSA). The PRV2 model we propose responds to the demand for a simple, reliable method and is a useful alternative for the calculation of liquid–vapour partition coefficients.