The characteristics of various fast pyrolysis oils, based on diverse sources of biomass, were investigated. The studied pyrolysis oils were products of the Karlsruhe Bioliq process, supplemented by some purchased samples. The quantification of water content and viscosity of the samples were determined by conventional analyses. Various NMR techniques were examined with respect to their applicability as tools for process analysis of the pyrolysis products. Low-field NMR spectroscopy (medium-resolution NMR, MR-NMR) combined with PLS-R was used for determination of the water concentration. In addition, two diffusion NMR approaches were investigated: pulsed field gradient (PFG-)NMR and single-sided NMR. Correlations of the diffusion coefficients resulting from both methods, with viscosity and water concentration, showed the suitability of the methods for process analysis in this context. All three NMR approaches were found to be advantageous for the characterization of pyrolysis oils by their water content and viscosity. Due to their technical robustness, MR-NMR and single-sided NMR were found to be promising tools for (online) process analysis in the pyrolysis process.