Abstract: Carbon dioxide free of many impurities is formed by combusting syngas with oxygen and controlling the amount of oxygen combined with the syngas so that the produced combustion gas has less than 2% unreacted oxygen. The syngas can be formed in a horizontal reactor 10 which combusts fuel with oxygen in the presence of water to form a hot gas stream which contacts a carbon feed stock introduced into a reaction zone 23 to form syngas. This is collected in a residence chamber 18, which has a gas outlet 20 leading directly to the syngas burner 75 located in the combustion chamber 71.