Procedure designed to determine properties of a gas mix containing hydrocarbons, wherein said gas mix particularly comprises natural gas or biogas, wherein said procedure comprises the following steps: The gas mix is allowed to flow through a measuring arrangement; Determination of a pressure- and temperature-dependent thermal conductivity value , an associated temperature measured value and an associated pressure measured value of the flowing gas mix; Determination of a hydrogen proportion of the gas mix on the basis of the thermal conductivity value, the associated temperature measured value and the associated pressure measured value; Determination of a pressure- and temperature-dependent density measured value , an associated temperature measured value and an associated pressure measured value of the flowing gas mix; Determination of a value for the average molar mass or the standard density of the gas mix on the basis of the density measured value, the associated temperature measured value and the associated pressure measured value; Determination of a value for the average molar mass or the standard density of a residual gas mix reduced by the hydrogen proportion on the basis of the average molar mass or the standard density of the gas mix and the hydrogen proportion; Determination of a pressure- and temperature-dependent viscosity measured value , an associated temperature measured value and an associated pressure measured value of the flowing gas mix; Determination of a value for the Wobbe index of the residual gas mix on the basis of the viscosity measured value, the associated pressure measured value and the associated temperature measured value; Determination of a first value for the calorific value of the residual gas mix on the basis of the average molar mass or the standard density of the residual gas mix and the Wobbe index of the residual gas mix. The gas mix is allowed to flow through a measuring arrangement; Determination of a pressure- and temperature-dependent thermal conductivity value , an associated temperature measured value and an associated pressure measured value of the flowing gas mix; Determination of a hydrogen proportion of the gas mix on the basis of the thermal conductivity value, the associated temperature measured value and the associated pressure measured value; Determination of a pressure- and temperature-dependent density measured value , an associated temperature measured value and an associated pressure measured value of the flowing gas mix; Determination of a value for the average molar mass or the standard density of the gas mix on the basis of the density measured value, the associated temperature measured value and the associated pressure measured value; Determination of a value for the average molar mass or the standard density of a residual gas mix reduced by the hydrogen proportion on the basis of the average molar mass or the standard density of the gas mix and the hydrogen proportion; Determination of a pressure- and temperature-dependent viscosity measured value , an associated temperature measured value and an associated pressure measured value of the flowing gas mix; Determination of a value for the Wobbe index of the residual gas mix on the basis of the viscosity measured value, the associated pressure measured value and the associated temperature measured value; Determination of a first value for the calorific value of the residual gas mix on the basis of the average molar mass or the standard density of the residual gas mix and the Wobbe index of the residual gas mix. <EOS>