NOVELTY - The method comprises saturating gas from the reactor at 250-900 degrees C with a first hydrocarbon based fluid in a first upstream cleaning step and absorbing the remaining tars with a second hydrocarbon based fluid in a second cleaning step. The first hydrocarbon based fluid comprises aromatic hydrocarbons corresponding with the tars to be removed. The first mixture of tars resulting from the first cleaning step and first fluid are fed to a first separation step from the second fluid based on evaporation temperature of the related fraction.    USE - The method is useful for gasifying of biomass in a reactor at of 600-1300 degrees C and purifying the gas flow by removal of tars from the gas flow.    ADVANTAGE - The method is capable of efficiently gasifying biomass in the reactor by rapidly removing tars from the gas flow thus effectively purifying the gas flow in an economical manner.    DETAILED DESCRIPTION - The method comprises saturating gas from the reactor at 250-900 degrees C with a first hydrocarbon based fluid in a first upstream cleaning step and absorbing the remaining tars with a second hydrocarbon based fluid in a second cleaning step. The first hydrocarbon based fluid comprises aromatic hydrocarbons corresponding with the tars to be removed. The first mixture of tars resulting from the first cleaning step and first fluid are fed to a first separation step from the second fluid based on evaporation temperature of the related fraction. The light fraction resulting from the first separation step is added to the gas flow from the reactor at the first cleaning step, where the heavy fraction is removed. The first mixture is entered in a buffer before the first separation step. A part of the first mixture is subjected to the first separation step and an other part from the buffer is reused for the first cleaning step. The gas is cleaned before the first cleaning step in a cyclone, and is cleaned between the first and second cleaning step by an electrostatic filter. A non-gaseous fraction resulting from the cyclone or electrostatic filter is supplied to the buffer. The viscosity from the fluid from the buffer is adjusted by the supply. The second fluid comprises linear hydrocarbons. An INDEPENDENT CLAIM is included for a system for gasifying biomass.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a system for gasifying biomass.    Biomass (1)    Reactor (3)    First cleaning device (8)    Buffer (13)    Electrostatic filter. (15)