In this short note we address a key issue regarding the time evolution of the surface tension of droplets that are made up of gasoline and alcohol blends. The burning process, and thus its efficiency and exhaust gas composition, in any combustion system (including SI and CI combustion engines) is strongly affected by the basic characteristics of the fuel spray. The droplets' size and size uniformity are two of the more important properties. Smaller droplets will evaporate, mix, and burn faster than larger ones. Reliable evaluation of the droplets' size in terms of the injection pressure, injector geometry, and the fuel properties is an essential tool for the combustion chamber designer. In this context, a major fuel property is the surface tension of the fuel. Here we show how the surface tension of a fuel droplet may vary with time during its injection process, thus affecting its size. The surface tension variation is mainly attributed to the molecular mobility of the surfactant while the liquid/gas interface grows. We present some measurements of the dynamic surface tension of gasoline/alcohol blends and compare them to the equilibrium value. We used the maximum bubble pressure method to determine the dynamic surface tension. Gasoline with an octane number of 95 was used as the basic fuel to be mixed in different proportions with ethanol or methanol.