Hypervisor vendors do claim that they have negated virtualization overhead compared to a native system. They also state that complete guest isolation is achieved while running multiple guest operating systems (OSs) on their hypervisors. But in a virtualization environment which is a combination of hardware, hypervisor and virtual machines (VMs) with guest operating systems, there bound to be an impact on each guest operating system while other guest operating systems are fully utilizing their allotted system resources. It is interesting to study hypervisor’s guest isolation capacity while several guest operating systems running on it. This paper selected three hypervisors, namely ESXi 4.1, XenServer 6.0 and KVM (Ubuntu 12.04 Server) for the experimentation. The three hypervisors are prudently preferred as they represent three different categories (full virtualized, para-virtualized, and hybrid virtualized). Focus being on hypervisors’ guest isolation capacity evaluation, therefore, private cloud is chosen over public cloud as it has fewer security concerns. Private Cloud is created using apache’s CloudStack. Windows 7 OS is deployed as a guest VM on each hypervisor and their guest isolation capacity is evaluated for CPU and Network performances.