Abstract Ignition delay times have been measured behind reflected shock waves at 1.5, 12 and 30 atm for a mixture representative of a syngas produced from biomass (0.29659% CO/0.29659% H 2 /0.15748% CO 2 /0.08924% CH 4 /0.20997% H 2 O/0.95013% O 2 in 98% Ar (mol.%)) and for the same biomass-derived syngas mixture doped with 200 ppm of NH 3 . The importance of the various constituents on the ignition delay time was investigated by comparing the results with data from various baseline mixtures (H 2 /O 2 /Ar, H 2 /CO/O 2 /Ar and H 2 /CO/O 2 /Ar with one of the other constituent of the syngas ( i.e. CO 2 , H 2 O, CH 4 or NH 3 )). The equivalence ratio was set to 0.5 during this study. Several recent detailed kinetics mechanisms from the literature were computed against these data, with fair agreement. Results showed that the mixture composition can have an important effect on the ignition delay time, with most of the effect being due to CH 4 addition through the reaction CH 4 + OH ⇄ CH 3 + H 2 O. The ammonia impurity had very little effect on the ignition delay time over the range of conditions studied.