A field experiment of carbon dioxide (CO2) storage in underground coal seams with simultaneous (enhanced) production of coalbed methane production was set up and performed in the upper Silesian coal basin in Poland. The main aim of this project was to investigate the technical and economic feasibility of this type of CO2 storage under European conditions. An existing coalbed methane well was cleaned up, repaired, and put back into production in May 2004 to establish a baseline production. A new injection well was drilled 150 m (492 ft) away from the production well. This distance was chosen to establish a breakthrough of the injected CO2 into the production well to learn as much as possible from the operations. Initial injection of CO2 occurred in August 2004 in three seams of Carboniferous age in the depth interval between 900 and 1250 m (3117 and 4101 ft). Several actions were taken to establish continuous injection, which was eventually reached in April 2005 after stimulation of the reservoir by a frac job. In May 2005, approximately 12–15 t/day were injected in continuous operations. Compared to baseline production, the production of methane increased significantly because of the injection activities. Recovery of methane is, however, low, which is probably related to low diffusion rates into and out of the coal. Nevertheless, a total of 692 t of CO2 are stored in the reservoir, most likely because of adsorption of CO2 on the coal. The results provide good hope for successful future upscaling of the operations, although further research is required. The realization of an onshore pilot for CO2 storage can possibly help to overcome start-up barriers of future CO2 storage initiatives in Europe.