TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Condition: The near-critical water is preferably at 220-245 atm and 350-375degreesC. The heavy hydrocarbons and the required amount of biomass are mixed in a stirred tank at 100-140, preferably approximately 120degreesC at ambient pressure, and pumped at 225-250 atm, in which the mixture of heavy hydrocarbon and biomass is combined and mixed with feed water pumped at the same pressure, the combined mixture being heated to the requested reactor of 370-380degreesC and then introduced into the reactor having a fixed bed catalyst, preferably as rings or another geometry, causing as little pressure difference across the fixed bed catalyst, the fixed bed catalyst being group 4b element, preferably zirconium, and especially potassium carbonate, which is introduced into the reactor through the feed water, the hot effluent from the reactor being passed through heat exchangers for preheating the reactor feed and cooling the effluent, which is subjected to pressure reduction, and then final cooling and phase separation into an aqueous phase, which may be recirculated to the process with the feed water, and the product phase consisting of lighter hydrocarbons. Preferred Component: The group 4b element is zirconium, especially in the form of its dioxide. The group 1a element is potassium, especially in the form of its carbonate. Preferred Composition: The potassium is added at 0.1-10, preferably 0.5-5 wt.%. EXAMPLE - Boscan heavy crude oil, bitumen and the light hydrocarbons produced from internal standards (gasoline, kerosene and diesel) were analyzed with gas chromatograph equipped with a flame ionization detector and a capillary splitter. Simulated distillation was performed in accordance with American Society for Testing and Materials (ASTM) D2887. The autoclave was filled with 3x3 mm zirconia tablets, then a mixture of 100 cm3 heavy oil and 10 wt.% saw dust which was preheated to 90degreesC, was poured into the autoclave. Finally, 200 cm3 containing 1 wt.% potassium as potassium carbonate was added to the autoclave. The autoclave was closed and pressure tested. Within 40 minutes, it was then heated to the requested temperature, kept at this temperature for 4 minutes, and then cooled to approximately 150degreesC. The autoclave contents were removed from the inside. The remaining reaction products on the outside and inside of the catalyst were removed by pulverizing the catalyst tablets and extracting the powder with tetrahydrofuran. After removing the tetrahydrofuran by distillation, the residue was mixed with the main liquid reaction product from the autoclave. This product (the effluent) was separated in an aqueous phase and a hydrocarbon phase. The latter was analyzed for American Petroleum Institute (API), simulated distillation and metal content. The following results were obtained: API: 28degreesC, 5 ppm nickel, 12 ppm vanadium, and simulated distillation: more than 95 wt.% was boiling below 524degreesC.