A simple procedure for the evaluation of the pressure coefficient d gamma/dP (gamma, surface tension; P, pressure) at a liquid-gas interface is described. This method is based on thermodynamics, and the final equation is d gamma/dP = E(s)/P-i, where E(s) represents the total surface energy of the pure liquid and P-i is its internal pressure. About 50 fluids have been investigated and the results are discussed. The numerical values of the coefficient d gamma/dP for common liquids at room temperature and atmospheric pressure range from 1.3 to 2.3 x 10(-8) cm. However, for water and mercury the coefficients are higher. A physical interpretation of the volume-surface area coefficient is attempted.