The article examines membrane permeabilization and the consequent content release of lipid vesicles due to the addition of surfactant. Experimental results show that content release involves a complex kinetics where almost instantaneous release is followed by prolonged slow leakage. The model proposed therefore regards bilayer permeability as varying with the time elapsed from the moment of surfactant addition. A delta function followed by an exponentially decaying profile is assumed for these permeability curves. The effects of surfactant concentration and type (Triton X-100, Tween 20 and Tween 60) can be compared by comparing the fitting parameters of the permeability curves.