A method for determining a buffer effect of an activated carbon filter for a tank venting system of a fuel container for hydrocarbon-containing fuels involves feeding a defined quantity of hydrocarbon molecules to the activated carbon filter (320) via a tank connection (320_1) of the activated carbon filter (320) by a hydrocarbon feed system (310). A carrier gas flow is introduced into the activated carbon filter (320) via an air connection (320_2) of the activated carbon filter (320), and a defined volumetric flow is sucked out of the activated carbon filter (320) via an engine connection (320_3) of the activated carbon filter (320) by a hydrocarbon measuring device (340), and its content of hydrocarbon molecules is measured. The defined quantity of hydrocarbon molecules is made available by the hydrocarbon feed system (310) in the form of a thermodynamically isolated gas quantity.