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The use of 2-chloro-4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaphospholane followed by 31P-NMR ana lysis has been frequently employed to quantitatively characterize the structure of hydroxyl groups in lignin and, more recently, biodiesel. This technique serves as a valuable tool to determine aliphatic hydroxyls, phenolics and carboxylic acid groups in lignin and aliphatic hydroxyl groups in partially substituted glycerols. This study demonstrates the application of this analytical technique to pyrolysis oils to allow efficient analysis and identification of important functional groups present in bio-oils and the measurement of moisture content. Phosphitylation followed by 31P-NMR ana lysis was used to show that the moisture content of the loblolly pine bio-oil used in this study was 11.94%. The results also established that the biooils obtained from loblolly pine cellulose had higher levoglucosan content than the bio-oil obtained from the starting pine itself. In addition, the total phenolic content of bio-oil derived from loblolly pine milled wood lignin was greater than that obtained from the bio-oil from the loblolly pine cellulose. The data also highlighted the ability to track chemical transitions that take place during pyrolysis using 31P-NMR.