Described are methods and systems for dynamically reallocating memory amongst virtual machines executing within a virtualization environment. A computer can execute a virtualization environment that can include one or more virtual machines and that can include a memory manager. The memory manager can dynamically reallocate memory by identifying a maximum and minimum memory value for each virtual machine, determining a target memory value for each virtual machine using the maximum and minimum memory value, and identifying one or more virtual machines that have an actual memory usage value that is less than the target memory value calculated for those virtual machines. To re-allocate the memory, the memory manager can allocate additional memory to the identified virtual machines by inflating a balloon driver, then de-allocate the additional memory, and reallocate the de-allocated, additional memory to other virtual machines within the virtualization environment.