In order to improve fairness and stability of TCP best-effort service we propose a new congestion control algorithm using packet loss information obtained from Selective Acknowledgments (SACK), and evaluate its effectiveness by simulation. The proposed scheme is for an environment consisting of Random Early Detection (RED) routers which drop each arriving packet with a certain probability after a threshold. The proposed mechanism adjusts the decrease in congestion window for Fast Recovery and the increase in congestion window per ACK during the congestion avoidance phase according to the number of lost packets. Simulation results show that not only the bandwidth allocation fairness is improved but also throughput deviation is markedly reduced resulting in more stable transport capability.