This document summarizes a study on improving the efficiency of resource utilization in virtual infrastructure for high-throughput computing. The study proposes a pre-staging model where virtual machine images are pre-loaded on execution nodes and jobs are directly submitted to the virtual machines. Experimental results show that the pre-staging model improves job execution times by 10-15 times compared to using Condor's virtual universe, with greater improvements for non-HPC jobs. The overhead of virtualization also reduces performance gains for HPC jobs like MPI applications.