This paper is research in progress on an extension of the Unified Theory of Acceptance and Use of Technology (UTAUT) to web systems usage for e-procurement. Focusing on business-to-business transactions, this research explores an extended version of the UTAUT that integrates core drivers and deterrents of web systems usage and investigates the consequence of such usage on corporate buyers. Data collected from 136 corporate buyers from over 120 organizations helped with the validation of the instrument. Intermediary results from a cluster analysis show differences among respondents that improve our understanding web-based procurement practice.