Mobile Ad hoc Networks (MANETs) have become increasingly popular in many applications including emergency search and rescue operations due to their ease of installation and low setup cost, and more importantly their support for users' mobility. MANETs consist of a collection of self-organized wireless mobile devices that can temporary form a network without the aid of any pre-established infrastructure or centralized administration. The exchange of information is often carried out through multiple hops, thus many routing protocols have been specifically developed for this purpose, e.g. Destination-Sequenced Distance Vector (DSDV), Ad hoc On-Demand Distance Vector (AODV) and Dynamic Source Routing (DSR). Network simulation tools have been increasingly used to analyze the performance of MANETs routing protocols. In order to capture realistic scenarios, simulators have been extended to include a realistic radio wave propagation model that represents the wireless channel used in the study. Different radio propagation models have been proposed over the past years where each one is suitable for a certain environment. Generally, propagation models can be divided into two main categories, large-scale path loss and small-scale fading. Most commonly used propagation models in the MANETS simulation tools fall in the large-scale category, e.g. Free Space and Two Ray Ground. This research presents a comprehensive performance evaluation of the well-known Dynamic Source Routing (DSR) protocol under different large-scale radio propagation models. Three propagation models have been considered, notably Free Space, Two Ray Ground and Shadowing. The network simulator NS-2 has been used to evaluate the performance of DSR under different scenarios. Our simulation results demonstrate that the use of different radio propagation models has a considerable impact on the performance of the DSR protocol. Moreover, DSR does not perform well under all propagation models when the network conditions become stressful, e.g. heavy congestion and high mobility. The results also reveal that while the Free Space model provides the best performance in terms of network throughput, packet delivery ratio and routing overhead while varying node mobility, traffic load and network size conditions, the Two Ray Ground model presents better performance for a varying transmission range.