In some applications of WSNs some nodes are more likely to generate important data. By setting higher priorities to these nodes, they send data sooner than other nodes by reducing the contention delay. We consider some senders and a receiver in their neighbourhood while one sender has a higher priority than other nodes. We analyse and formulate two concepts: delay and efficient data rate. Simulation results show that a network with prioritised nodes send more important data in a real time manner. Also average delay of sending data in a prioritised network is less compared with equal-priority nodes network.