Abstract: The network lifetime optimization issue is investigated for bidirectional two-hop cooperative Orthogonal Frequency Division Multiplexing (OFDM) systems recruiting multiple relays. Since direct treatment for the network lifetime maximization formulation is not feasible, a suboptimal strategy is proposed, which takes energy pricing concept for each node into account. Specifically, the power allocation for each subcarrier, relay, and source selection is optimized gradually rather than deriving jointly optimal solutions. Actually, by applying standard Lagrange technique, the optimal power assignment for each source/relay pair, which minimizes the total energy cost subject to limited transmission power and network throughput constraints, can be readily solved. An optimum relay is then selected out accordingly among all possible pairs, finally the direction of traffic flows can be determined by choosing the link with smaller price sacrifice. Two practical scenarios are considered, i.e., a direct source-destination link is available or not while implementing the proposal. Moreover, when the direct link can be fully exploited, the impact of two diversity combining techniques including Maximal Ratio Combining (MRC) and Selective Combining (SC) on the power allocation optimization is theoretically derived. Simulation results indicate that, the network lifetime by utilizing the proposed algorithm outperforms the existing approaches significantly.