In this paper, a unified analytical model is established to analyze the performance of backoff schemes in IEEE 802.11 DCF networks under saturation condition. It is shown that BEB suffers from deteriorated queueing performance due to a large second moment of access delay, and a key to reduce the second moment lies in the growth rate of the backoff window size. Quadratic Backoff (QB) is further proposed, with which the backoff window size is quadratically increased upon collisions. Both the theoretical and simulation results show that QB can achieve a comparable throughput with that of BEB, but with much better queueing performance.