© 2021 The Authors. Published by American Chemical Society.This work investigated the co-gasification of biomass and coal chars obtained from fast pyrolysis (1000 °C, ~104 °C s-1) in a drop tube furnace. Olive residue and Soma lignite were fast-pyrolyzed in a drop tube furnace, and different char blends were prepared for co-gasification at different temperatures (800, 900, 950, and 1000 °C) in a thermogravimetric analyzer. The chars obtained from the drop tube furnace were analyzed for their chemical and mineral composition, morphology, surface area, and particle size distribution. Three distinct blends of olive residue and Soma lignite chars were prepared in the (biomass-coal) ratios of 50.50, 25.75, and 10.90. Three kinetic models were fitted to the (co)gasification profiles: the volumetric model, the grain model, and the random pore model. The results showed that fast pyrolysis strongly affected the morphology and surface area of the chars, which were not the decisive factors influencing the gasification behavior. Biochar displayed the presence of K in an active form (K2Ca(CO3)2 and KCl), which had a catalytic effect on the gasification. Synergies during the co-gasification were observed for ratios of biochar above 25%, whereas the 10.90 blend showed a similar gasification behavior to that of the lignite char. The results strongly suggested the existence of a threshold for K/Al and K/Si in the char blend for which synergies can be observed, which coincided with the 25OR-75SL blend, specifically, K/Al = 0.7 and K/Si = 0.4.