With the enormous growth in telecommunication industry, energy efficiency has become a critical issue. Base stations account for a significant portion of the energy budget of a cellular network. Traditional energy saving techniques switch some base stations off completely during light loads to save energy. This creates problems for the backhaul network and also for quickly returning to full capacity when demand increases. In this paper, we propose a novel technique called cell zooming to reduce energy consumption at base stations. With cell zooming, base stations dynamically adjust their coverage radius and hence their transmit powers based on user locations. The transmit power is set to the minimum required level depending on user locations and signal to interference and noise ratio (SINR) required. Base stations are never completely switched off. Simulations show that the proposed cell zooming algorithm reduces the energy consumption of base stations by up to 40% without compromising the quality of service (QoS) for users compared to traditional static-coverage-area base stations.