Bubble formation in surfactant solutions is frequently encountered in systems of practical importance but has seldom been investigated systematically. In this work a simple modified two-stage spherical model, by which the dynamic surface tension at the bubble surface plays a role, was developed for bubble formation under constant-flow conditions. Equilibrium and dynamic surface tension data and the values of bubble volume at detachment were obtained experimentally for aqueous solutions of sodium dodecyl sulfate and Triton X-100, The predicted results are shown to agree well with experimental ones, especially for concentrations less than the critical micelle concentration. This implies that the surface relaxation phenomenon is important for bubble formation in surfactant solutions. For accurate prediction of bubble formation in surfactant solutions, dynamic surface tension rather than equilibrium data should be taken into consideration.