Trees from the genus Boswellia (Burseraceae) are traditionally used as a medicine, a fumigant, in various cosmetic formulations and in aromatherapy in several countries around the world. This plant produces a commercial oil known as frankincense which has a woody, spicy and haunting smell. Frankincense oil has several pharmacological properties, of which many elude to the anti-infective potential. Variation in the chemical composition of this oil has been reported in literature. These factors prompted an investigation to study the commercial frankincense oils from various international suppliers. Twenty essential oils were analyzed by gas chromatography coupled to mass spectrometry. Considering the major constituents, the oils were found to be qualitatively similar. However, there was immense quantitative variation for certain oil constituents. The components identified and their range in the oils include α-pinene (2.0-64.7%); α-thujene (0.3-52.4%); β-pinene (0.3-13.1%); myrcene (1.1-22.4%); sabinene (0.5-7.0%); limonene (1.3-20.4%); p-cymene (2.7-16.9%) and β-caryophyllene (0.1-10.5%). The antimicrobial activity (minimum inhibition concentration assay) of the oils was investigated against five reference test organisms and the activity ranged from 4-16 mg/ml (Staphylococcus aureus); 1.5-8.3 mg/ml (Bacillus cereus); 4.0-12.0 mg/ml (Escherichia coli); 2.0-12.8 mg/ml (Proteus vulgaris) and 5.3-12.0 mg/ml (Candida albicans).