This paper introduces a novel two-phase broadcast scheme referred to as collaborative rateless broadcast (CRBcast). CRBcast is a scalable approach for reliable and energy-efficient broadcasting in a multihop wireless sensor networks that also addresses load balancing, while requiring no knowledge of network topology. CRBcast combines the energy-efficiency offered by probabilistic broadcasting (PBcast) with the reliability features offered by application-layer rateless coding. In the first phase of CRBcast, packets encoded using a rateless code are dispersed into the network based on PBcast. In the second phase, simple collaboration of neighboring nodes ensures that all nodes recover original data with a very high probability of success. Since the performance of CRBcast rests heavily on that of PBcast, first part of this paper analyzes both analytically and via simulations the probabilistic broadcasting scheme. We then study the effectiveness of CRBcast. We show that CRBcast provides both reliability and energy efficiency simultaneously. Simulation results indicate that CRBcast provides an energy savings of at least 72% and 60% in comparison with flooding and PBcast, respectively.