Designers of oxy-natural gas burners until now relied heavily on engineering experience and numerous experimental tests when developing new oxy-combustion technology. This is due both to the scarcity of comprehensive experimental data in semi- and full industrial-scale combustion systems and to the limited capabilities of present CFD codes whose predictions cannot be used with confidence to assist in the furnace/burner design process. To address these gaps in the knowledge, a consortium of eight companies viz. AGA, Air Liquide, Gaz de France, Hoogovens Corporate Services b.v., Linde AG, Nippon Sanso Corporation, Tokyo Gas Co. Ltd. and the IFRF, has initiated the OXYFLAM project, to collect a comprehensive set of data to help in the understanding of the structure of oxygen-natural gas flames, the design of pure-oxygen burners and the validation of CFD computer codes for pure oxygen-natural gas flames. The project began in 1995 and deals both with the detailed characterization of oxy-natural gas burners and with the validation of new computer codes as sub-models for oxy-natural gas flame calculations. The experimental work includes extensive input-output and detailed measurements in flames in the thermal input range 0.7-1.0 MW. This paper presents some of the experimental results collected throughout the project. The emphasis is on the flame structure, heat transfer and NOx emissions characteristics of the flames studied.