The species-selection problem is particularly challenging for high-temperature low-pressure systems, where many of the reactions involve "well-skipping", so there is more than one transition state between the reactant(s) and the major products of a reaction. To deal with this issue, RMG includes an extension of the rate-based algorithm for chemically-activated reactions that was originally invented by Matheu , then improved by Allen and Goldsmith , and recently further improved by Johnson and Grinberg Dana . The numerical/computational challenges can be severe for systems with a large number of important isomer wells; often there are so many possible isomers that it is difficult for a human to correctly enumerate them all, much less judge which are important at particular reaction conditions. Several research groups have been working on aspects of this problem; particularly notable is the automated Potential Energy Surface (PES) search software package KinBot developed by Zador and co-workers .