Host virtualization has become of great interest as it is a technology that can enable the implementation of cloud computing. For this, it can offer several benefits, such as high levels of sharing of computing resources, ubiquitous availability, and savings on hardware investment. Although it has been claimed that host virtualization can also offer the benefit of energy savings, the levels of savings are unknown. In this paper, we present experimental evaluations of energy expenditure of virtual machines used for computation processes. We measure the energy spent by a number of virtual machines and compare it to the energy spent by a single and multiple (real) Linux hosts. The results show that the virtual machines deliver similar performance to processes run in real machines for small loads, and achieve significant energy savings for a modest number of users. Therefore, it is then expected that there is a number of VMs for what energy savings is optimal. The values also indicate that workstations optimized for virtualization can offer significant benefits.