The main factors that influence the value of surface tension of a liquid measured with the Maximum Pressure Bubble Method are critically evaluated. We present experimental results showing the effect of capillary diameter, capillary depth, bubble spheroidicity and liquid density at room temperature. We show that the decrease of bubble spheroidicity due to increase of capillary immersion depth is not sufficient to explain the deviations found in the measured surface tension values. Thus, we propose a simple experimental procedure that allows determining the surface tension of a liquid without any previous knowledge of its density. This procedure is especially useful when the liquid of interest exhibits variations of surface tension and density with time, as for example during condensation reactions to obtain SiO2 sols from a tetraethyl ortosilicate (TEOS) solutions during their aging process.