Essential oils of 11 populations of Thymus mastichina (L.) L, 10 populations of Salvia lavandulifolia Vahl and 12 populations of Lavandula latifolia Medik., collected in full bloom during 3 years (2009-2011) were analyzed by gas chromatography (GC)-flame ionization detector (FID) and mass spectrometry (MS) to study the variability among populations and the influence of the year of harvest in the essential oil composition. One factor ANOVA for population origin and year of harvest, and Principal Component Analyses (PCA) using the main compounds as set of observations were carried out for each species. For T. mastichina all the samples were 1,8-cineol chemotype (58.52-68.82%), however the linalool content showed a great range of variation (1.16-10.24%). 1,8-Cineol (6.21-33.69%), camphor (2.85-22.44%) and beta-pinene (5.11-19.85%) were the main compounds for S. lavandulifolia and 1,8-cineol (30.57-54.09%) and linalool (15.82-45.94%) for L. latifolia essential oils. Populations from T. mastichina and S. lavandulifolia from different years appeared mainly grouped in the PCA figures while L. latifolia populations showed no clustering. T. mastichina was the least environmentally influenced species, showing mainly differences among populations. S. lavandulifolia also had small differences among campaigns and higher differences within populations. Conversely, L. latifolia showed a higher percentage of differences in the volatile composition depending on the year of harvest but genotypic variability was also observed. In conclusion, the variability of the essential oil composition is largely dependent on the population studied having genetic factors a greater influence than the environmental factors. However, environmental factors are also influencing the essential oils composition and must be taken into account. (C) 2015 Elsevier B.V. All rights reserved.