In this paper we describe the xrootd file access system, designed in collaboration between the Stanford Linear Accelerator Laboratory (SLAC)1, USA and Istituto Nazionale di Fisica Nucleare (INFN), Padova, Italy. The system was designed to provide access to over 10^7 files representing several petabytes of experimental physics data. We analyze the agent-based query algorithm employed by this system to provide a scalable means of locating files that are scattered across a very large file server cluster. In the process we introduce the concept of a passive bidding scheme and describe its relationship to file serving commitments as a way to substantially reduce message traffic.