This paper presents a pronking controller for our six-legged robot RHex. Development of the controller begins with a passive-dynamics approach, ensuring that the robot is naturally suited to running. Running with flight phase is then achieved using only proprioceptive (joint angle sensing only) feedback for touchdown detection and for tracking fixed joint reference trajectories. Body pitch oscillation is attenuated by means of an open loop leg speed change during stance. The robot achieves speeds of about two body lengths per second with a specific resistance of 1.85.