The concentrations and enantiomeric purity of the major monoterpene constituents in a number of Melaleuca alternifolia (tea tree) oils have been determined by enantioselective gas chromatography. Consistent enantiomeric ratios of 65:35 (+:-) for terpinen-4-ol and 76:24 (+:-) for α-terpineol were observed for the range of oils analyzed. Attempts to validate these ratios in the intact oil by ¹H NMR together with chiral lanthanide shift reagents have not yet been successful. ¹H NMR was, however, successful in confirming the enantiomeric purity determined by gas chromatography of standard terpinen-4-ol [79:21 (+:-)] and α-terpineol [35:65 (+:-)] samples. Under the correct conditions, a single analysis on a β-cyclodextrin column enables the determination of the quality of the oil as set forth by the Australian standard and provides additional enantiomeric evidence of the authenticity of the oil.