NOVELTY - A biomass feedstock and a conventional petroleum feedstock are co-processed by liquefying at least a portion of a biomass-catalyst mixture comprising solid biomass particles and a catalyst in a first reaction vessel, to produce a liquefied biomass feedstock; and co-processing at least a portion of the liquefied biomass feedstock and the conventional petroleum feedstock in a conventional refinery unit. The solid biomass particles have individual sizes below 1500 mu m.    USE - Method for co-processing a biomass feedstock and a conventional petroleum feedstock (claimed) to produce fuel including light gases (ethane, propane, or butane), naphtha, or distillates (jet fuel, diesel, or heating oil); and specialty chemicals including light olefins (ethylene, propylene, or butylene), acids (formic or acetic), aldehydes, alcohols (ethanol, propanol, butanol, or phenol), ketones, or furans.    ADVANTAGE - The method can reduce equipment cost, energy cost, and/or degradation or undesirable reaction of conversion product, and increase the availability of fuel and/or specialty chemicals derived from biomass. Further, the preparation of the biomass for co-processing in conventional petroleum refinery units can have a synergistic effect, reducing the temperature necessary for catalytic or pyrolytic conversion of the biomass and/or increasing the conversion efficiency of the biomass, and facilitating processing in conventional refining units.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) an apparatus for co-processing a biomass feedstock and a conventional petroleum feedstock, comprising a first conventional refinery unit comprising a biomass-catalyst mixture and used for liquefying at least a portion of the biomass-catalyst mixture to produce a liquefied biomass feedstock; and a second conventional petroleum refinery process unit comprising the liquefied biomass feedstock and the conventional petroleum feedstock, where the second conventional petroleum refinery unit is for co-processing at least a portion of the liquefied biomass feedstock and the conventional petroleum feedstock;    (2) a biomass feedstock for co-processing with a conventional petroleum feedstock in a petroleum refinery unit comprising a biomass-catalyst mixture; and    (3) a biomass-conventional petroleum feedstock for co-processing in a conventional petroleum refinery process, comprising a liquefied biomass feedstock derived from liquefying a biomass-catalyst mixture; and a conventional petroleum feedstock.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a catalytic cracking system including two risers and a catalyst cooler.    Catalytic cracking system (100)    Risers (105, 110)    Strippers (115, 120)    Knock out drum (125)    Regenerator (130)    Catalyst cooler (135)