NOVELTY - Method comprises providing a biomass conversion system comprising a pressurization zone (4) and a digestion unit (2), providing a cellulosic biomass at a first pressure, introducing at least a portion of the biomass into the pressurization zone and then pressurizing the zone to a second pressure i.e. higher than the first pressure, transferring at least a portion of the biomass from the zone to the digestion unit at a third pressure and digesting at least a portion of the biomass in the digestion unit to produce a hydrolyzate comprising soluble carbohydrates within a liquor phase.    USE - The method is useful for converting cellulosic biomass (claimed) into biofuels including synthetic gasoline, diesel fuels and jet fuels, where the biomass includes corn stover, straw, bagasse, Miscanthus, Sorghum residue, switch grass, bamboo, water hyacinth, hardwood, hardwood chips, hardwood pulp, softwood, softwood chips, softwood pulp, leaves, roots, seeds, stalks, agricultural wastes (e.g. corn stalks, straw, seed hulls, sugarcane leavings and nut shells), wood materials (e.g. wood or bark, sawdust, timber slash and mill scrap), municipal waste (e.g. waste paper, yard clippings or debris) and energy crops (e.g. poplars, willows, switch grass, alfalfa, prairie bluestream, corn and soybeans).    ADVANTAGE - The method enables energy-efficient conversion of biomass into biofuel in an economical manner.    DETAILED DESCRIPTION - Method comprises providing a biomass conversion system comprising a pressurization zone (4) and a digestion unit (2) that are operatively connected to one another, providing a cellulosic biomass at a first pressure, introducing at least a portion of the cellulosic biomass into the pressurization zone and then pressurizing the pressurization zone to a second pressure i.e. higher than the first pressure, transferring at least a portion of the cellulosic biomass from the pressurization zone to the digestion unit at a third pressure i.e. less than or equal to the second pressure but higher than the first pressure and digesting at least a portion of the cellulosic biomass in the digestion unit to produce a hydrolyzate comprising soluble carbohydrates within a liquor phase. An INDEPENDENT CLAIM is included for a biomass conversion system comprising a loading mechanism, a pressurization zone, and a digestion unit that are operatively connected to one another in sequential series, a fluid circulation loop establishing fluid communication between an inlet and an outlet of the digestion unit and a fluid transport line establishing fluid communication between the fluid circulation loop and the pressurization zone, where the pressurization zone and the digestion unit are operatively connected to one another in a manner such that the portion of the cellulosic biomass in the pressurization zone is transferred to the digestion unit, while the digestion unit is operating at a pressure of at least 30 bar.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a biomass conversion system.    Digestion unit (2)    Pressurization zone (4)    Pressure vessel (5)    Loading vessel (6)    Valves. (8)