The NASA Orbiting Carbon Observatory (OCO) will make space-based measurements of atmospheric carbon dioxide (CO2>) with the precision, resolution, and coverage needed to characterize regional scale CO2> sources and sinks and quantify their vari¬ability over the seasonal cycle. This mission will be launched in December 2008 and will fly in a 705 km altitude, 1:26 PM sun-synchronous orbit that provides complete coverage of the sunlit hemisphere with a 16-day ground track repeat cycle. OCO carries a single instrument designed to make co-boresighted spectroscopic measurements of reflected sunlight in near-infrared CO2> and molecular oxygen (O2>) bands. These CO2> and O2> measurements will be combined to provide spatially resolved estimates of the column averaged CO2> dry air mole fraction, XCO2>. The instrument collects 12 to 24 XCO2> soundings/second over the sunlit portion of the orbit, yielding 200 to 400 soundings per degree of latitude, or 7 to 14 million soundings every 16 days. Existing studies indicate that at least 10% of these soundings will be sufficiently cloud free to yield XCO2> estimates with accuracies of ~0.3 to 0.5% (1 to 2 ppm) on regional scales every month.