 The global characteristics of retrievals of the column-averaged CO2 dry air mole fraction, XCO2, from shortwave infrared observations, has been studied using the expected measurement performance of the NASA Orbiting Carbon Observatory II, OCO2, mission. For nadir observations, we find single-sounding retrieval errors with values typically less than one part per million, PPM, over most land surfaces. Larger errors are found over snow slash ice and ocean surfaces due to their low albedo. This article was authored by Charles Miller, David Crisp, Brian Connor, and others.