Reliable data for biogenic carbon dioxide (CO2) emissions are needed for carbon emission trading and in order to provide more accurate inventories. When combusting mixtures of fuels from fossil or biogenic origin, it is often difficult to determine the exact ratio of biogenic and fossil CO2 in the total CO2 in the exhaust gas of stationary sources, because the biogenic and fossil composition of the combusted fuels is not always known or cannot be determined with sufficient accuracy. The contribution of solid, liquid or gaseous biofuels to energy production will increase. A reliable and robust method for the determination of the ratio of fossil and biogenic CO2 in the emitted exhaust gas can enhance the application of these fuels, as reliable data for carbon emission trading can be generated for carbon emission trading. The standard DIN EN ISO 13833 specifies measurement methods for the determination of the ratio of biomass- and fossil-derived carbon dioxide (CO2) in the CO2 from exhaust gases of stationary sources, based on the radiocarbon 14C isotope) method. The procedures for the determination of the radioactive carbon isotope (14)C include accelerated mass spectrometry (AMS), beta-ionization (BI), and liquid scintillation (LS) measurement procedures. The lower limit of application is a biogenic to total CO2 fraction of 0,02. The methods are applicable in a biogenic CO2 fraction between 0,02 and 1,0. This standard is of interest for industry and measurement institutes.