— This paper develops a distributed, threshold based MAC protocol for cooperative Multi Input Multi Output (MIMO) transmissions in distributed wireless systems. The protocol uses a thresholding scheme that is updated dynamically based on the queue length at the sending node to achieve low power transmissions while ensuring stability of the transmission queues at the nodes. Simulation results are provided to evaluate the performance of the proposed protocol and compare it against regular point to point as well as fixed group size cooperative MIMO MAC protocols.