The rising of a gas bubble in a surfactant solution is considered within the framework of the rear stagnant cap (r.s.c.) model at low Reynolds number. The adsorption is supposed to be the slowest process in the system. The bubble velocity is predicted to depend on time due to the nonstationary process of surface stagnant zone formation. Various types of bubble behavior are discussed. It is shown which information on the characteristics of adsorption one can extract from the time dependency of the bubble velocity.