The physical properties of crude bio-oils preclude their direct use as fuel. Specifically, their high oxygen content results in undesirable acidity and poor thermal stability. Therefore, the removal of oxygen is essential for the use of bio-oils as fuel. Currently, the most straightforward method for application of bio-oil as fuel is through blending with petroleum feeds. Emulsions have been explored extensively for the introduction of polar bio-oils into nonpolar petroleum feeds. Coprocessing of deoxygenated oils and petroleum feeds by fluid catalytic cracking (FCC) is another method for blending bio-oil with petroleum. Because the deoxygenated oil is less polar, it can be directly added to a petroleum feed, after which the blend is processed by FCC to further reduce the oxygen content and crack larger hydrocarbons. Here, a hydrodeoxygenated bio-oil (HDO bio-oil) is blended with a light gas oil (LGO) and then hydrotreated. The oil is characterized at each step throughout the blending process by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS) and two-dimensional gas chromatography (GCxGC) MS. FT-ICR MS showed no changes in elemental compositions resulting from the blending processes. After hydrotreating the blend, there is a reduction in the carbon number and double-bond equivalents (DBE = number of rings plus double bonds to carbon) as well as the removal of sulfur and oxygen species. GCxGC MS showed that the alkanes in the blend and hydrotreated blend are contributed by the LGO, whereas cycloalkanes originate from the HDO bio-oil. Removing oxygenated species and reducing DBE of the HDO biooil through blending and hydrotreatment provide an oil with a composition suitable as fuel.