Currently cellular networks are overloaded, due to rapid growth of various smartphone applications. With the arrival of 3G and 4G network technologies mobile data traffic has been growing at an unprecedented pace and increasingly surpassing the network capacity. Mobile data offloading is an effective network congestion demotion approach to solve the overload issue through opportunistic communication. It is a beneficiary approach, because there is no monetary cost for it. Subscribe Send Architecture and Opportunistic forwarding protocol plays a vital role during offloading by allowing users to subscribe the contents but does not download the subscribed content on the Content Service Provider thereby network traffic reduces up to a greater extent. A quantitative study on performance evaluation of opportunistic routing protocols like Epidemic, Spray and Wait, ProPhet and MaxProp are discussed in this paper. We have compared these protocols based on few performance metrics like overhead ratio, delivery probability and average latency. Our simulation results verify that MaxProp performs well and can offload cellular traffic effectively.