A new indirect method for measuring the level of beta-methyl-gamma-octalactone precursors in oak wood by GC-MS is described. This level is calculated from the difference between the amount of free beta-methyl-gamma-octalactone and the amount formed after hydrolysis and lactonization. It is compared to the level of a precursor of cis-beta-methyl-gamma-octalactone, a 6'-O-gallate derivative of (3S,4S)-4-[3-beta-glucopyranosyloxy-3-methyloctanoic acid, determined directly by HPLC. These two methods are applied to 12 powdered samples of Sessile oak wood and the results show that the 6'-O-gallate derivative of (3S,4S)-4-beta-D-glucopyranosyloxy-3-methyloctanoic acid is by far the most abundant precursor of beta-methyl-gamma-octalactone in this wood.