Résumé : Existing Medium Access Control protocols for Wireless Sensor Networks reduce the radio activity to improve network lifetime, at the expense of a reduced network capacity. Those protocols are ill-suited for energy constrained sensor networks that must support spatially and temporally heterogeneous traffic loads. This paper proposes a novel multi-ressource allocation algorithm and describes its implementation as a medium access control protocol for Wireless Sensor Networks. The algorithm, named Cascading Tournament (CT), is a localized, dynamic, joint contention/allocation algorithm. It relies on cascading iterations of tournaments to allocate a multiplicity of ressources to a multiplicity of winners. CT-MAC is an implementation of CT as a medium access protocol. By allocating multiple logicals channels allocation at each competition, CT-MAC improves the network capacity at a given duty-cycle or decreases the energy expenditure of the MAC layer at a given network capacity. Extensive simulations highlight the benefits of CT-MAC in both single-hop and multiple-hop scenarios through the computation of relevant performance metrics: power consumption, network capacity, delay and retransmissions. CT-MAC offers an unprecedented trade-off between network capacity, energy efficiency and delay and stands out as a solid candidate for energy constrained sensor networks that must support heterogeneous traffic loads. Our simulations show that CT-MAC significantly outperforms the state-of-the-art SCP-MAC protocol.