Wireless Sensor Networks have been deployed for various purposes like military applications, surveillance in volcanic or remote regions, etc. But one of the major challenges in Wireless Sensor Network (WSN) that is yet to be sorted out is the lack of energy efficiency which retards the lifetime of the network. In this paper, we propose an approach that can be deployed for small sensor networks to achieve maximum energy efficiency using a single mobile sink. The mobile sink does not have a wide range as a base station but has a rechargeable battery and so it can act as a collector for getting data from sensor nodes and transmitting it to base station via internet or cellular network. We have analysed the optimum speed of the mobile sink for minimal delay. The proposed approach includes clustering followed by data gathering and forwarding by mobile sink. In this paper, we evaluate and compare network performance using delay parameter upon varying the speed of the mobile sink. Knowing the number of sensor nodes and its distribution in the network, there is a need to ensure that the energy wastage is minimal with acceptable levels of delay depending on the application. We have compared the energy efficiency of the proposed approach with that of the traditional approach in this paper. © Springer-Verlag Berlin Heidelberg 2011.