It has previously been shown that an investment in a black liquor gasification (BLG) plant is advantageous regarding efficiency and economic performance compared to a new recovery boiler investment for pulp mills. However, the availability of black liquor is limited and strongly connected to the pulp production. This limits the maximum production capacity and requires high availability of the BLG plant to ensure that the crucial cooking chemicals in the black liquor can be returned to the pulp mill. One alternative to increase the motor fuel production volumes and improve the operational flexibility of the BLG plant is to add pyrolysis oil to the black liquor feed and co-gasify the blend. Furthermore, the catalytic alkali metals in the black liquor enhance the conversion rates in a reactor, leading to a higher syngas quality achieved at lower temperatures when gasifying a blend compared to unblended pyrolysis oil. The objective of this study was to techno-economically investigate the opportunity to increase methanol production at a pulp mill via co-gasification of pyrolysis oil and black liquor. Gasifying a blend consisting of 25% pyrolysis oil and 75% black liquor on wet mass basis nearly doubles the methanol production, compared to gasifying the available black liquor only. For a 50/50 blend the methanol production increases by more than 250%. According to published data, pyrolysis oil can be bought to a cost around 70 €/MWh. This corresponds to an increase in IRR for the investment in the 25/75 and the 50/50 blend case with 4%-units and 6%-units, respectively, compared to the IRR (17.5%) for the BLG plant. Co-gasification of black liquor and pyrolysis oil is an attractive investment opportunity that will increase the methanol production volume and add extra revenues per produced unit compared to methanol produced via gasification of pure black liquor.