Equilibrium calculations of three problems regarding biomass combustion, at various levels of sophistication, were performed at six laboratories using seven combinations of computer programs and databases. The objective was to test the adequacy of the programs and databases for calculating both condensed and gas-phase behavior. The first problem was a simplified calculation for the combustion of a woodlike material with added sulfur to possibly form an ideal molten salt solution of potassium and calcium sulfate. The second and third problems were to simulate aspen wood and wheat straw combustion, respectively, and required a relatively sophisticated database on high-temperature solutions to describe condensed phases. All the participants performed calculations of the gas phases, which were reasonably accurate when their databases were adequate. For problem I, most of the participants were also able to calculate a reasonable set of condensed phases. However, for problems II and III, only four of the participants, using the two most Sophisticated computer programs and databases, had the ability to produce rational results for the condensed phases. This round robin identified two computer programs and their associated databases that could prove useful for calculating the condensed-phase equilibrium chemistry of biomass combustion when coupled with experimental programs and the capability to expand databases as new experimental data become available. Such calculations can greatly enhance our understanding of the total equilibrium chemistry of biomass combustion.