In this paper we study the problem of long-term capacity adequacy in electricity markets. We implement a dynamic model in which firms compete for investment and electricity production under imperfect Cournot competition. The main aim of this work is to compare three investment incentive mechanisms: reliability options, forward capacity market and capacity payments. Apart from the oligopoly case, we also analyze collusion and monopoly cases. Dynamic programming is used to deal with the stochastic environment of the market and mixed complementarity problem and variational inequality formulations are employed to find a solution to the game. The main finding of this study is that market-based mechanisms would be the most cost-efficient mechanism for assuring long-term system capacity adequacy. Moreover, generators would exert market power when introducing capacity payments. Finally, compared with a Cournot oligopoly, collusion and monopolistic situations lead to more installed capacities with market-based mechanisms and increase consumers' payments. doi: 10.5547/ISSN0195-6574-EJ-Vol32-No4-6