As the most widely used reliable transport in today's Internet, TCP has been extensively studied in the past. However, previous research usually only considers a small or medium number of concurrent TCP flows. 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 a large number of concurrent TCP flows. First, we develop a simple yet realistic network model to abstract an Internet connection. Based on the model, 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 and derive general conclusions about overall throughput, goodput, and loss probability.