One of the main limitations that still keeps Wireless Sensor Networks (WSNs) from being adopted in a large scale is the limited energy supply, i.e. the lifetime of the nodes that constitute the network. The wireless communication between nodes is responsible for most of the energy consumed in WSNs. A promising method to improve the energy efficiency is the usage of a Cooperative Multiple Input Multiple Output (CO-MIMO) scheme, where nodes form clusters to transmit and receive signals using a virtual antenna array. This work presents a study on the energy consumption of multi-hop and single-hop transmission compared to CO-MIMO and how to select the most efficient method. It also proposes a method for adaptively choosing the number of nodes that form a CO-MIMO cluster in order to maximize the lifetime of the network and to avoid disconnections. The proposed method takes into account not only the total energy consumption but also the distribution of energy within the network, aiming to keep the energy distribution across the network as uniform as possible. The effects of the proposed methods in the total available energy of the network and in the distribution of the energy is presented by means of numerical simulations. © 2016 IEEE.