Disaster response systems (DRSs) assist responders by providing a wide range of services. These services are usually implemented as distributed applications (overlays) capable of operating in an infrastructure-less underlying network such as MANETs. However, all the services in DRSs may not be equally critical. For instance, the communication between firefighters is certainly more important than the communication between news reporters. Ensuring the reliability and the quality of the required vital services is a key to successful disaster response operations. We propose a differentiated QoS architecture for overlay-based DRSs to enforce a prioritization scheme between overlays as well as between users within overlays. Our architecture provides self-organizing distributed admission control and policy enforcement services. We have run extensive simulations to evaluate the performance of our architecture. The results show that our architecture not only enables differentiated QoS, it also improves overall QoS in terms of the number of successful overlay flows. © 2014 IEEE.