NOVELTY - Producing an aqueous solution of carbohydrates comprising 6C-sugar-containing oligomers, 6C-sugar monomers, 5C-sugar-containing oligomers and/or 5C-sugar monomers, comprises (a) reacting biomass or a biomass-derived reactant with a solvent system comprising (i) an organic solvent consisting of beta -, gamma -, and/or delta -lactones and (ii) water in the presence of an acid catalyst to yield a product mixture, and (b) adding a solute to the product mixture to cause partitioning of the product mixture into an aqueous layer and a immiscible organic layer.    USE - The method is useful for producing an aqueous solution of carbohydrates comprising 6C-sugar-containing oligomers, 6C-sugar monomers, 5C-sugar-containing oligomers and/or 5C-sugar monomers from biomass (claimed) such as lignocellulosic biomass for the production of biofuel and bioproduct production process, where the carbohydrate includes arabinose, lyxose, ribose, ribulose, xylose, xylulose, allose, altrose, fructose, galactose, glucose, gulose, idose, mannose, psicose, sorbose, tagatose, and talose.    ADVANTAGE - The method is capable of effectively producing the aqueous solution of the carbohydrates from the lignocellulosic biomass with high selectivity and yield and without maximum degradation of carbohydrate monomers.    DETAILED DESCRIPTION - Producing an aqueous solution of carbohydrates comprising 6C-sugar-containing oligomers, 6C-sugar monomers, 5C-sugar-containing oligomers and/or 5C-sugar monomers, comprises (a) reacting biomass or a biomass-derived reactant with a solvent system comprising (i) an organic solvent consisting of beta -, gamma -, and/or delta -lactones and (ii) at least 1 wt.% water in the presence of an acid catalyst for a time and under conditions to yield a product mixture, and (b) adding a solute to the product mixture in an amount sufficient to cause partitioning of the product mixture into an aqueous layer and a substantially immiscible organic layer, where at least a portion of water-insoluble 6C-sugar-containing polymers or oligomers or water-insoluble 5C-sugar-containing polymers or oligomers, if present in the biomass or biomass-derived reactant, are converted to water-soluble 6C-sugar-containing oligomers, 6C-sugar monomers, 5C-sugar-containing oligomers and/or 5C-sugar monomers.