In this paper, we propose a new IEEE 802.11-based MAC protocol for ad hoc networks. The protocol incorporates multiple transmit power options in the MAC layer by letting stations adaptively select the transmit power, and thus vary the coverage area. It is shown that the protocol is capable of improving network latency, which is a fundamental QoS measure. The latency reduction factor is more than two under low and moderate load conditions, and close to one at high offered loads, when compared to the standard IEEE 802.11 DCF MAC protocol. This reduction in latency is achieved with almost no decrease in network throughput.