A method of gasification by introducing a feed material to be subjected to gasification into a dual fluidized bed gasifier comprising a pyrolyzer fluidly connected with a combustor such that a circulation stream comprising a heat transfer material can be continuously circulated between the pyrolyzer, in which the temperature of the circulation stream is reduced, and the combustor, in which the temperature of the circulation stream is increased, wherein the pyrolyzer is operable to convert at least a portion of the feed material into a gasifier product gas comprising hydrogen and carbon monoxide, and wherein the combustor is operable to increase the temperature of the circulation stream via combustion of char introduced thereto with the circulation stream and at least one supplemental fuel. A system for carrying out the method is also provided.