NOVELTY - Upgrading a bio-oil, comprises: contacting the bio-oil with an olefin in the presence of a catalyst to form an upgraded bio-oil, which has, compared to the bio-oil, one or more of a reduced hydroxyl value, a reduced acid value, a reduced polarity, a reduced miscibility in a polar solvent, a reduced oxygen concentration, a reduced water concentration, or an increased average molecular weight; providing (502) a vapor phase bio-oil; and contacting (504) the vapor phase bio-oil with the olefin.    USE - The method is useful for upgrading a bio-oil in a vapor phase (all claimed).    ADVANTAGE - The upgraded bio-oil: has improved miscibility with hydrophobic fuels; and increases the bio-oil solubility in fuels such as diesel without undesirable attributes.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) converting a pyrolysis oil to one or more hydrocarbon fuel range products, comprising (a) reacting a pyrolysis oil with a feed comprising an olefin in the presence of a catalyst to form a product mixture comprising at least one of an esterification product and an etherification product, and (b) contacting the esterification product and the etherification product in a reaction zone with a hydrotreating catalyst in the presence of hydrogen under reaction conditions sufficient to convert at least a portion of the esterification product and the etherification product into one or more fuel range hydrocarbon products;    (2) the upgraded bio-oil produced by a process;    (3) a composition comprising one or more hydrocarbon fuel range products, where the mixture of one or more hydrocarbon fuel range products is produced from a pyrolysis oil by the process;    (4) improving miscibility of the bio-oil in a hydrophobic fuel, comprising providing the miscible bio-oil, where the miscible bio-oil is upgraded, catalytic, or upgraded and catalytic compared to a starting material bio-oil, and contacting the miscible bio-oil to a hydrophobic fuel to form a miscible mixture, where the miscible bio-oil is characterized by greater miscibility in the hydrophobic fuel compared to the bio-oil starting material;    (5) a bio-oil composition comprising a miscible ternary mixture according to each triplet of miscible or partly miscible ranges as given in the figure 7A, 7B, 7C, or 7D of the specification; and    (6) the bio-oil, an upgraded bio-oil, a catalytic bio-oil, or an upgraded catalytic bio-oil in a percentage according to each corresponding range, an alcohol in a percentage according to each corresponding range of 1-butanol, and a hydrophobic fuel in a percentage according to each corresponding range of diesel.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a method for upgrading a bio-oil in a vapor phase.    Providing a vapor phase bio-oil (502)    Contacting the vapor phase bio-oil with an olefin in the presence of a catalyst to provide an upgraded bio-oil. (504)