One alternative to reduce the motor fuel production cost and improve the operational flexibility of a black liquor gasification (BLG) plant is to add pyrolysis oil to the black liquor feed and co-gasify the blend. The objective of this study was to investigate techno-economically the possibility to increase methanol production at a pulp mill via co-gasification of pyrolysis oil and black liquor. Gasifying a blend consisting of 50% pyrolysis oil and 50% black liquor on a wet mass basis increases the methanol production by more than 250%, compared to gasifying the available black liquor only. Co-gasification would add extra revenues per produced unit of methanol (IRR > 15%) compared to methanol from unblended BLG (IRR 13%) and be an attractive investment opportunity when the price for pyrolysis oil is less than 70 €/MW h. The economic evaluation was based on a first plant estimate with no investment credit for the recovery boiler and a methanol product value volumetric equivalent to conventional ethanol, both these conditions will not applicable when the technology has been fully commercialized.