The effect of fuel structure on emissions must be better known to promote cleaner combustion of solid fuels. In commercial combustors initial slow pyrolysis steps produce emission of numerous possible organic species. Biomass is today also considered for upgrading by pyrolysis to bio-oils. Knowledge of slow pyrolysis processes of coal and biomass is limited. We have designed a miniature pyrolysis reactor suited for GC/MS analysis. In the evaluation of the approach three distinct solid fuels were investigated: bituminous coal, sawdust from spruce and chips from eucalyptus. Coal pyrolysis produced high amounts of alkanes, naphthalenes and PAH. Coal also produced alkyl substituted phenols. Sawdust from spruce produced almost the same species as eucalyptus. However, the product distributions from spruce- and eucalyptus pyrolysis differed. The products from eucalyptus were significantly more substituted than the products from spruce. The products from wood samples were dominated by oxygenates: fatty acids, cyclic oxygenates and methoxy substituted phenols. The present approach can be used for selecting solid fuels suitable for clean combustion and production of bio-oils.