The integration of a fluidized bed fast pyrolysis process producing bio-oil to an existing fluidized bed boiler combined heat and power (CHP) plant is presented. The purpose of this work is to assess the cost and performance of the integrated fast pyrolysis bio-oil production compared to a stand-alone fast pyrolysis bio-oil production plant. The reason for integrating bio-oil production into a fluidized bed boiler is to increase overall energy efficiency and profitability and to decrease the production costs of the bio-oil. In the integrated fast pyrolysis concept hot sand from the fluidized bed boiler is used for heating the fast pyrolysis reactor. Simultaneously, fast pyrolysis process byproducts such as char and noncondensable gases are cofired in the CHP boiler together with the primary forest residue boiler fuel. The assessment shows that the integration decreases the primary fuel requirement of the boiler. The integration causes changes in the net power and heat output of the CHP plant, but the integration can still be more profitable than a stand-alone fast pyrolysis process. The differences in pyrolysis feedstock characteristics are important when comparing integration to stand-alone bio-oil production. In this work pine sawdust and forest residue feedstock were evaluated, of which only the forest residue proved to be economically advantageous for integration to a CHP boiler. The advantage is evaluated as a reduction in bio-oil production cost compared to a stand-alone fast pyrolysis process for bio-oil production. For implementation of the integrated process, three potential industrial strategies for boiler operation in combined heat and power plants were assessed. These include keeping the superheated steam mass flow constant, keeping the boiler flue gas mass flow constant, and keeping the electricity output constant. The total integrated process efficiency was 87% for the case of sawdust and 86.2% for the forest residue. Sensitivities were studied for variations in the cost of forest residue boiler fuel, cost of heat, and cost of electricity and for the variations in the capital expenditure benefits obtained due to the integration. It was shown that the advantage of integration is highly sensitive to the cost of heat, primarily because of the energy-intensive pyrolysis feedstock drying. The feedstock cost is also a major factor in estimating the advantage of integration. Utilizing forest residue as feedstock for fast pyrolysis proved to be advantageous in all cases evaluated in this work, whereas the break-even price for a competitive integration utilizing sawdust feedstock is 25 (sic)/MWh. The most beneficial operational integration strategy for the boiler would be to maintain a fixed flue gas flow (exhaust) from the boiler, resulting in an advantage of integrated oil production (reduced bio-oil production cost) compared to stand-alone bio-oil production of 7.9 (sic)/MWh bio-oil. The integrated sawdust case, which is shown to be less competitive in this study, would lead to an additional production cost compared to the stand-alone bio-oil production cost of 1.6 (sic)/MWh bio-oil. The results obtained in this study are independent of process scale.