One step thermal conversion of lignin to gasoline range liquid products was accomplished by pyrolyzing softwood (SW) kraft lignin with select zeolites at 600 °C. Gel Permeation Chromatography (GPC) and Nuclear Magnetic Resonance (NMR) including quantitative 13C, 31P-NMR and Heteronuclear Single-Quantum Correlation (HSQC)-NMR were used to characterize various pyrolysis oils. By employing a zeolite catalyst aliphatic hydroxyl groups decreased by 70–100% in the resulting bio-oil and the content of carboxylic acid groups also decreased by 44–85% in comparison to a control pyrolysis oil generated with no additive. Of the additives studied MFI and MOR zeolites provided the best in situ decarboxylation of bio-oils. The results of 13C-NMR indicated after the use of FAU and BEA zeolites, the pyrolysis oils contained ∼80% less methoxy groups than the native pyrolysis oil, and almost all the oxygen (up to ∼87%) belonged to phenolic hydroxyl groups. In addition, the average molecular weight of these two upgraded pyrolysis oils decreased by ∼60% with respect to the control pyrolysis oil and they had a molecular weight profile in the gasoline range (80–120 g mol−1). By adding MFI, FAU and BEA zeolites, the pyrolysis oils contained some polyaromatic hydrocarbons (PAH). In contrast, there were very limited amount of PAH in FER and MOR upgraded pyrolysis oils and almost no PAH in the native pyrolysis oil.