NOVELTY - The computerized method comprises storing, in memory, a first set of carbon flow values characterizing the production and use of a biofuel derived from a first fraction of an agricultural biomass, storing, in memory, a second set of carbon flow values characterizing the production and use of a co-product from a second fraction of the agricultural biomass, calculating a regulatory value for the biofuel from the first and second sets of carbon flow values using the data processor, and trading the biofuel having the regulatory value and a tradable credit.    USE - The computerized method is useful for accounting carbon flows and for determining a regulatory value for a biofuel such as ethanol using a data processor having a memory.    ADVANTAGE - The computerized method is capable of accurately accounting carbon flows and determining a regulatory value without anthropogenic greenhouse gas emissions thus reducing the carbon intensity and improving the sustainability performance of the biofuels.    DETAILED DESCRIPTION - The computerized method comprises storing, in memory, a first set of carbon flow values characterizing the production and use of a biofuel derived from a first fraction of an agricultural biomass, storing, in memory, a second set of carbon flow values characterizing the production and use of a co-product from a second fraction of the agricultural biomass, calculating a regulatory value for the biofuel from the first and second sets of carbon flow values using the data processor, and trading the biofuel having the regulatory value, a tradable credit generated as a function of the regulatory value, or the biofuel and the tradable credit. The second fraction comprises an agricultural residue. The co-product mitigates anthropogenic greenhouse gas emission. The co-product comprises: electricity, heat and power; and a cellulosic biofuel, solid biofuel, biochar, bio-chemical, bio-plastic, building material, construction material, paper pulp, animal feed and soil amendment, prevents carbon from the second fraction from flowing to the atmosphere, and is a substitute for a fossil hydrocarbon product for preventing carbon from a fossil hydrocarbon product from flowing to the atmosphere. The production and use of the co-product comprises producing electricity from second fraction and/or coal. INDEPENDENT CLAIMS are included for:    (1) a method of engineering a carbon cycle for biofuel production and use; and    (2) a method of manufacturing a biofuel.    DESCRIPTION OF DRAWING(S) - The diagram shows a flow chart of a biofuel production process.