NOVELTY - Converting a polysaccharide to a commodity chemical comprises: (a) contacting the polysaccharide, where the polysaccharide is optionally derived from biomass, with a polysaccharide degrading or depolymerizing metabolic system; and (b) contacting the suitable monosaccharide or oligosaccharide with commodity chemical biosynthesis pathway, where the commodity chemical biosynthesis pathway comprises an aldehyde or ketone biosynthesis pathway.    USE - The methods, recombinant microorganisms, and microbial systems are useful for converting a polysaccharide to a commodity chemical; for converting the polysaccharide to the suitable monosaccharide or oligosaccharide; for converting the suitable monosaccharide or oligosaccharide to a first commodity chemical; for converting the suitable monosaccharide or oligosaccharide to the commodity chemical; and for producing the commodity chemical enriched refinery-produced petroleum product (all claimed).    ADVANTAGE - The methods are economic and provide technically simple process for converting biomass into hydrocarbons for use as biofuels or biopetrols.    DETAILED DESCRIPTION - Converting a polysaccharide to a commodity chemical comprises: (a) contacting the polysaccharide, where the polysaccharide is optionally derived from biomass, with a polysaccharide degrading or depolymerizing metabolic system, where the metabolic system is selected from; (i) enzymatic or chemical catalysis, and (ii) a microbial system, where the microbial system comprises a recombinant microorganism, where the recombinant microorganism comprises one or exogenous genes that allow it to grow on the polysaccharide as a sole source of carbon, thus converting the polysaccharide to a suitable monosaccharide or oligosaccharide; and (b) contacting the suitable monosaccharide or oligosaccharide with commodity chemical biosynthesis pathway, where the commodity chemical biosynthesis pathway comprises an aldehyde or ketone biosynthesis pathway, thus converting the polysaccharide to the commodity chemical. INDEPENDENT CLAIMS are:    (1) a method for converting the polysaccharide to the suitable monosaccharide or oligosaccharide, comprising contacting the polysaccharide, where the polysaccharide is optionally obtained from biomass, with a microbial system for a time sufficient to convert the polysaccharide to the suitable monosaccharide or oligosaccharide, where the microbial system comprises: (i) at least one gene encoding and expressing an enzyme selected from a lyase and a hydrolase, where the lyase and/or hydrolase optionally comprises at least one signal peptide or at least one auto-transporter domain; (ii) at least one gene encoding and expressing an enzyme selected from a monosaccharide transporter, a disaccharide transporter, a trisaccharide transporter, an oligosaccharide transporter, a polysaccharide transporter, and a super-channel; and (iii) at least one gene encoding and expressing an enzyme selected from a monosaccharide dehydrogenase, an isomerase, a dehydratase, a kinase, and an aldolase, thus converting the polysaccharide to the suitable monosaccharide or oligosaccharide;    (2) a recombinant microorganism that is capable of growing on the polysaccharide as a sole source of carbon, where the polysaccharide is selected from alginate, pectin, tri-galacturonate, di-galacturonate, cellulose, and hemi-cellulose;    (3) a method for converting the suitable monosaccharide or oligosaccharide to a first commodity chemical;    (4) a method for converting the suitable monosaccharide or oligosaccharide to the commodity chemical;    (5) a microbial system or recombinant microorganism;    (6) a commodity chemical produced by the methods;    (7) a blended commodity chemical comprising the commodity chemical and a refinery-produced petroleum product; and    (8) a method of producing the commodity chemical enriched refinery-produced petroleum product, comprising blending the refinery-produced petroleum product with the commodity chemical produced by the methods, thus producing the commodity chemical enriched refinery-produced petroleum product.