Abstract The essential oil of Grindelia humilis Hook et Arn (G.H.), G. robusta Nutt (G.R.) and G. squarrosa Dun F. (G.S.), were analyzed by GC/MS. Sixty-nine components were identified in the oil of G, humilis, representing 89.9% of the oil, while 56 components in the oil of G. robusta, and 68 components in the oil of G. squarrosa were identified representing 78.9% and 81.9% of the oils, respectively. The study revealed that the major components of the oil of G. humilis were polyacetylenes (46.2%) and germacrene D (11.9%). In contrast, the major components of G. robusta were oxygenated terpenoids (57.4%), of which borneol (14.8%) was the largest constituent. The oil of G. squarrosa was characterized by monoterpene hydrocarbons (47.7%), of which limonene (16.8%), Î±-pinene (16.1%) were the major components.