In the wake of the Paris Climate Agreement, there is an increasing need to monitor emissions from fossil fuel combustion around the world. For CO2 in particular, satellite imagers are being designed to observe the emission plumes from large point sources and intense urban area sources. To assess their potential, researchers in the CoCO2 project have tested a simple emission estimation scheme on the multi-year archive of the two NASA Orbiting Carbon Observatories (OCO-2 and OCO-3), which provide dense observations along the orbit line, but with a narrow swath.