In recent years, there have been two major trends in the ICT industry: green computing and cloud computing. Green computing implies that the ICT industry has become a significant energy consumer and consequently, a major source of CO2 emissions. Cloud computing makes it possible to purchase IT resources as a service without upfront costs. In this paper, the combination of these two trends, green cloud computing, will first be evaluated based on existing research findings, which indicate that private clouds are the most green option to offer services. Hosting of private clouds can be outsourced, which allows companies to focus on their core competences. Furthermore, three case studies of state-of-the-art companies offering green hosting services are presented and incentives affecting their energy-efficiency development are analyzed. The results reveal that currently there is no demand in the market for green hosting services, because the only incentive for companies is low costs. Service providers should illustrate their greenness with transparent efficiency metrics, draw up green service level agreements and compete with greenness. Then it is up to end users to require more green web services and create derived demand for green cloud services and green hosting services.