The essential oil from the resin of Pistacia lentiscus L. var. chia (mastic gum), growing wild in the eastern Aegean island of Chios (Greece), was hydrodistilled and analysed by GC–MS and GC–FID. Mastic samples were hydrodistilled in the presence or absence of H3PO4. The results indicate that distillation in the presence of 10% H3PO4 doubled the yield of the essential oil (EO). A total of 46 compounds, accounting for 90.16–99.13% of the total volatile components of the essential oil, were detected and their percentage contents in the essential oil were determined. The compounds that predominate are α‐pinene (63.22–71.17%), β‐myrcene (16.60–18.09%) and β‐pinene (2.08–2.78%). These compounds were found in similar abundance in all samples, indicating that, at this concentration, H3PO4 does not react with the oil components during the distillation. The significant increase of the EO yield could make it more accessible to the food, cosmetic and pharmaceutical industry. Copyright © 2009 John Wiley & Sons, Ltd.