Biomass fast pyrolysis liquid, also known as bio-oil, is a promising renewable fuel for heat and power generation; however, implementing crude bio-oil in some current combustion systems can degrade combustion performance and emissions. Optimizing fuel properties to improve combustion is one way to solve this problem. There is currently limited information on the relationship between fuel properties and combustion performance and emissions of bio-oil. In this study, various hardwood-derived bio-oils with different fuel properties were tested in a pilot stabilized spray burner under the same flow conditions. The effect of solids, ash, and water contents of bio-oil as well as ethanol blending was examined. Steady-state gas phase and particulate matter emissions were measured. The results show that carbon monoxide and unburned hydrocarbon emissions correlate with the solids and ash fractions of bio-oil. Carbon monoxide and unburned hydrocarbon emissions decrease with both higher water and ethanol contents. Increasing the volatile content of fuel by blending in ethanol is shown to improve flame stability. The fraction of fuel nitrogen that is converted to nitrogen oxide emissions decreases with an increasing fuel nitrogen content. Also, the organic fraction of particulate matter emissions is found to be a strong function of the thermogravimetric analysis residue of the fuel. A conceptual model for bio-oil combustion is proposed that relates the fuel properties to the emissions.