NOx emission indices were experimentally measured for partially premixed laminar flames of five different H-2/CO/CO2 fuels over a wide range of equivalence ratios Through those fuels, the effects of H-2/CO ratio and CO2 concentration on NOx emissions, flame appearance, visible flame height and flame temperature are presented EINOx values increase when 1 0 <= Phi <= 16, then remain near the highest value, before decreasing slowly when 3 85 <= Phi <= infinity. The increase of the CO2 concentration reduces the EINOx for the whole range of equivalence ratios, while the increase in the H-2/CO ratio reduces the EINOx when Phi <= 2 0 and is inconsequential for richer mixtures The variation in flame temperatures approximates EINOx trends The variation of flame color from blue to orange when the H-2/CO ratio is increased might be explained by higher CO levels in by-product combustion (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd All rights reserved