New catalysts are being sought for the water gas shift (WGS) reaction in connection with distributed hydrogen generation. This quest would be aided by improved fundamental understanding of WGS catalysis. We, thus, present here a systematic theoretical approach, namely, Reaction Route (RR) Graph analysis, for developing a comprehensive understanding of the WGS reaction based on a detailed molecular mechanism with apriori kinetics. The RR Graphs follow flow network laws of Kirchhoff, so that they allow not only graphical depiction of the myriad pathways, but also a detailed flux analysis of the network. Thus, we utilize a 19-step mechanism and assemble it into a RR Graph, which is analogous to an equivalent electrical circuit. These steps were picked to be comprehensive without causing undue complexities. A simplification and pruning of the mechanism is then performed based on Kirchhoff's laws of current (rate) and potential (affinity). As a result, the dominant pathways as well as the rate-limiting steps become transparent. Three dominant pathways are found, eventually, yielding an 11-step simplified mechanism, from which a predictive rate expression is derived. This provides good agreement not only with the complete WGS mechanism, but also with our own experimental data on Cu. Prediction of WGS activity on other metals is also provided. (C) 2008 Elsevier B.V. All rights reserved.