The field of wireless sensor network is a booming research area and its use is expanding quickly. It consists of many small sensor nodes. These nodes are operated through battery. Network lifetime depends on energy consumption. Nodes are deployed in unattended area. Therefore, replacing the battery or power source is often impossible. Data transmission consumes more amount of energy and sensor nodes’ battery life is constrained. Consumption of energy is the most fundamental parameter to be considered in wireless sensor networks. Research is going on in designing less energy consuming protocol to enhance network lifespan. In this paper, we have shown the simulation results of several types of energy efficient routing protocols for analysis. Experimental results of LEACH, TEEN, DEEC, SEP, improved LEACH - iLEACH, improved TEEN - iTEEN, improved DEEC - iDEEC and improved SEP - iSEP protocols are conducted under the MATLAB Simulator. We have also discussed a few unresolved research questions in this field for future investigation.