An experimental study was carried out to identify the parameters controlling the burnout of coal particles when cofired with blast-furnace gas (BFG) under boiler conditions. The experiments were conducted in a bench-scale furnace with a base-fine coal cofired with various amounts of BFG. Results indicate that the burnout problems with BFG cofiring were due to the cooler flame temperatures and shorter residence times associated with the high inert content of BFG, and due to the fall in oxygen partial pressure for the coal particles because of the early consumption by BFG. The data also suggest that the base-line coal is a low-reactivity fuel. Five candidate coals were tested, and they indicated that a significant improvement in carbon conversion could be achieved with more reactive coals. One coal was selected and subsequently tested in the boiler, and yielded consistent results.