Carbon dioxide (CO2) emissions from combustion sources are uncertain in many places across the globe. Here, we estimate CO2 emission rates from a small number of collocated observations from the Orbiting Carbon Observatory-3 (OCO-3) and the Earth Surface Mineral Dust Source Investigation (EMIT), both onboard the International Space Station (ISS). These near-simultaneous measurements allow for an unprecedented comparison of two unique space-based CO2 sensors over both isolated coal-fired power plants and multi-source scenes in China. We estimate CO2 emission rates using integrated mass enhancement and a Gaussian plume model. Where validation data is available, 15 of the 19 estimated emission rates have errors less than 37%. For the multi-source scenes, EMIT can estimate emissions from individual facilities but its aggregate emissions are 33% lower than OCO-3, likely because it cannot detect small sources or diffuse emissions. OCO-3, with its excellent precision, may better constrain CO2 emissions over the entire scene.