The problem of developing tools for the stimulation system of socially optimal actions (volunteering) is considered. Based on the study of the population’s differentiation according to the propensity to an altruism, the game-theoretic model of the social group’s
behavior is formed, accounting for the incentives for volunteering. In the cases of the linear decreasing incentive function and the linear cost functions of agents, the Cournot-Nash equilibrium mechanism in the corresponding game is proved. An existence of the equilibrium actions and an impact of incentives on the volunteers’ time distribution are confirmed by the simulation of the volunteers’ behavior in Russia.