Driven by the need to improve energy efficiency and reduce environmental impact, we observe a thrust towards enabling a Smart Grid. It is envisaged that to achieve these goals, the Smart Grid will be equipped with communications infrastructure and mechanisms that will enable near real-time control of the grid components. One of the key elements of the Smart Grid is the advanced metering infrastructure (AMI) which is expected to facilitate the transport of meter readings from a smart electricity meter at the customer premises to the utility provider, and control data in the other direction. These communications can be potentially realized by deploying a self-organizing mesh network composed of smart metering nodes connected to concentrator nodes which in turn are connected to the utility provider data management systems. This paper explores a cooperative communications approach to improve reliability of such mesh networks. The proposed opportunistic forwarding protocol called 'ORPL' has been realized as an enhancement on top of the routing protocol for low power and lossy networks, a connectivity enabling mechanism in AMI mesh networks. In ORPL, smart meter nodes select multiple candidate relays to facilitate reliable transport of smart metering data to the concentrator node. Moreover, it is designed to work in a distributed manner thereby ensuring scalability. We also present a further extension to ORPL, i.e., ORPLx with adaptive medium access control retransmit limit, which reduces unnecessary retransmissions. Our protocols have been evaluated and verified with comprehensive experimental results, demonstrating their effectiveness and favorable characteristics.