Failure data on mobile robots is critical for three reasons: to support the theory of autonomous fault detection, identification, and recovery necessary for success in new domains; provide design and manufacturing feedback to the robotics community; and permit project managers to accurately create development schedules. The failures considered in this paper occurred over a period of 2 years, in a variety of environments. Failure type and frequency data were collected from thirteen robots representing three manufacturers and seven models. The data was analyzed using standard manufacturing measures for the reliability of a product. The mean time between failures represents the average time to the next failure. Availability was used to gauge the impact of a failure on a project. The results show that the reliability for mobile robots is low, with an average MTBF of 8 hours and availability of less than 50%. The platform itself was the source of most failures (42%) for field robots, while the control system was responsible for 29% of the failures.