In this study, blends of biodiesel and softwood derived fast pyrolysis oil (FPO) were produced, characterized, and evaluated for thermodynamic and emission performance in a single cylinder research engine. FPO was supplied from an in-house fluidized bed reactor as well as a commercial source. Separate FPO-biodiesel blends from both FPO sources were prepared using initial volumetric ratios of 80:20 and 60:40 (biodiesel: FPO, by volume). After blending, mixing, and a 24 h settling period, two layers formed and the top, biodiesel-rich layers containing about 5 and 10 vol% FPO were decanted and characterized on the basis of a thermogravimetric analysis, viscosity, acid number, water content, elemental analysis, and heating value. Significant decreases in viscosity, acidity, and water content from the original FPO validated blending as means of extracting compounds suitable for use as fuels from pyrolytic liquids in biodiesel. A single cylinder, common rail, direct injection diesel engine was used to analyze the combustion performance of the FPO fuel blends against neat diesel and biodiesel. Fuel performance was characterized on the basis of a thermodynamic combustion analysis, as well as corresponding exhaust emission measurements for CO2, CO, unburned hydrocarbons, particulate matter, and NOx. Engine testing revealed similar indicated efficiencies for biodiesel and diesel at all considered engine operating modes, while blend fuels showed indicated efficiencies between 75 and 95% of diesel values. In general, FPO fuels exhibited increased ignition delays and shorter combustion durations with greater FPO blend concentrations, though this could be partially compensated for using a pilot injection strategy. The longer ignition delays of the blend fuels resulted in overly lean regions of the cylinder, which produced largely premixed combustion events contributing to brake specific CO and uHC emissions up to 1.5 and 3.5 greater than diesel, respectively. Specific PM emissions were 41-62% lower for blend fuels than diesel. Both blends of in-house FPO showed similar PM emission performance, however at higher concentration than low blend commercial fuel. (C) 2017 Elsevier Ltd. All rights reserved.