Producing a definitive picture of the CO oxidation reaction (CO + O-2 -> CO2) on Pt-group metals (Rh, Pd, Pt, and Ru) across the 'pressure gap' has proved to be a challenging task. Surface-sensitive techniques amenable to high pressure environments (e. g. PM-IRAS) have sparked a renewed interest in this reaction under realistic pressures. Here, we review recent work in our laboratory examining CO oxidation kinetics on Pt-group single crystals using PM-IRAS, XPS, and mass spectrometry from low (10 (8) - 10 (3) Torr) to high (1 - 102 Torr) pressures. These studies have shown that at both low and high pressures (a) Langmuir -Hinshelwood kinetics adequately describe CO oxidation kinetics on Pt-group metals (Pt, Pd, Rh) (i.e. there is no pressure gap) and (b) the most active surface is one with minimal CO coverage. Additionally, recent investigations of high pressure CO oxidation kinetics on SiO2 film supported Rh particles prepared in situ are discussed. (C) 2008 Elsevier B.V. All rights reserved.