This paper describes a series of experiments conducted with natural gas in air and in mixtures of oxygen and recycled flue gas, termed O-2/CO2 recycle combustion. The objective is to enrich the flue gas with CO2 to facilitate its capture and sequestration. Detailed measurements of gas composition, flame temperature and heat flux profiles were taken inside CANMET's 0.3 MWth down-fired vertical combustor fitted with a proprietary pilot scale burner. Flue gas composition was continuously monitored. The effects of burner operation, including swirling of secondary stream and air staging, on flame characteristics and NO, emissions were also studied. The results of this work indicate that oxygas combustion techniques based on O-2/CO2 combustion with flue gas recycle offer excellent potential for retrofit to conventional boilers for CO2 emission abatement. Other benefits of the technology include considerable reduction and even elimination of NOx emissions, improved plant efficiency due to lower gas volume and better operational flexibility. (C) 2002 Elsevier Science Ltd. All rights reserved.