This paper presents the throughput results obtained from a Wireless Sensor Network testbed, with single and multiple sources in different network deployments and routing architectures. The experimental testbed deployed at IIT Madras consisted of commercially available Crossbow TelosB and MicaZ nodes and a custom-built sensor node based on the DigiNet Xbee chip, with all nodes implementing the Zigbee standard. The networks were deployed in uniform grid topologies in three different deployments with up to 228 nodes. The main aim of the experiments is to analyze the throughput and packet delivery ratio observed with single and multiple sources. The experimental results show that delivery ratio reduces with increase in data rate due to collisions and help characterise the network capacity limits.