 The global characteristics of retrievals of the column-average 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. This study focuses on XCO2 retrieval precision and averaging kernels and their sensitivity to key parameters such as solar zenith angle, SZA, surface pressure, surface type and aerosol optical depth, AOD, for both nadir and sun glint observing modes. Realistic simulations have been carried out and the single-sounding retrieval errors for XCO2 have been derived from the formal retrieval error covariance matrix under the assumption that the retrieval has converged to the correct answer and that the forward model can adequately describe the measurement. Thus, the retrieval errors presented in this study represent an estimate of the retrieval precision. For nadir observations, we find single-sounding retrieval errors with values typically less than one part per million PPM over most land surfaces for SCAs less than 70 degrees and up to 2.5 PPM for larger SCAs. This article was authored by Charles Miller, David Crisp, Brian Conner and others. We are article.tv. Links in the description below.