As the most widely used reliable transport in today's Internet, TCP has been extensively studied in the past decade. However, previous research usually only considers a small or medium number of concurrent TCP connections. The TCP behavior under many competing TCP flows has not been sufficiently explored. In this paper we use extensive simulations to investigate the individual and aggregate TCP performance for large number of concurrent TCP flows. We have made three major contributions. First, we develop an abstract network model that captures the essence of wide-area Internet connections. Second, we study the performance of a single TCP flow with many competing TCP flows by evaluating the best-known analytical model proposed in the literature. Finally, we examine the aggregate TCP behavior exhibited by many concurrent TCP flows, and derive general conclusions about the overall throughput, goodput, and loss probability.