Abstract: Computational grids such as the Information Power Grid [1], Particle Physics Data Grid [2], and Earth System Grid [3] depend on TCP to provide reliable communication between nodes across a wide-area network (WAN). Of the available TCP implementations, TCP Reno and its variants are the most widely deployed; however, Reno's performance in computational grids is mediocre at best. Due to conflicting results in the evaluation of TCP implementations [4,5,6,7,8,9,10,11,12,13], we present a detailed simulation study that unifies the conflicting results and demonstrates the limitations of earlier work. We focus on the two most debated versions of TCP - Reno and Vegas. Using real traffic distributions, we show that Vegas performs well over modern high-performance links and better than Reno with the proper selection of the Vegas parameters alpha and beta. Our results exhibit ways to significantly enhance the performance of distributed computational grids that rely on TCP.