An adaptive algorithm for adjusting the gains of a vehicle speed control system is presented. By continuously adjusting the proportional-integral control gains, speed control performance can be optimized for each vehicle and operating condition. This helps the design of a single speed control module that does not need additional calibration or sacrifices in performance for certain car lines. It also allows improved performance for changing road conditions not possible with a fixed-gain control or other types of adaptive control. The results of initial vehicle testing confirm the performance improvements and robustness of the adaptive controller. >