Spectrum sensing is one of the critical aspects in cognitive radio (CR). CR user must be able to detect the spectrum opportunity reliably and efficiently in order to use the available spectrum. In spectrum sensing, a local radio might fail to monitor the available spectrum holes due to shadowing and hidden terminal problem. Cooperative spectrum sensing can be employed to combat this problem using two approaches; centralized and decentralized (distributed) system. In this paper, we evaluate the performance of both centralized and decentralized cooperative spectrum sensing under several policies; OR and AND rules based on energy detection. The effectiveness of the both centralized and decentralized techniques were investigated and compared in terms of probability of detection and signal-to-noise ratio (SNR). We observe that the OR rule achieve better performance than AND rule in attaining higher detection probability.