Abstract Within this paper, investigations to convert softwood with four different types of bed materials in the 100 kWth dual fluidized bed steam gasification pilot plant at TU Wien are presented and discussed. The results of ten different experiments were compared. Quartz, olivine and feldspar were mixed with limestone in mass ratios of 100/0, 90/10, 50/50 and 0/100. Limestone was used due to its catalytic activity at high temperatures as CaO and thus enhanced tar, char and water conversion of quartz, olivine and feldspar. The admixture of limestone to quartz, olivine and feldspar shifted the product gas compositions towards higher hydrogen and carbon dioxide and lower carbon monoxide contents. By using 100 wt.-% limestone as bed material a hydrogen content of 47.4 vol.-% could be generated. Additionally, the tar concentrations as well as the tar dew points decreased and especially the heavy tar compounds could be reduced. Already small amounts of limestone (