The composition of the volatile fraction of 236 samples of genuine Uruguayan lemon oils obtained by industrial processing during the 1992 and 1993 seasons was studied by GC. The samples were representative of all production areas situated in the North and South of the country. Forty-three components were identified in the oils. The quantitative data regarding all the samples were divided according to the production areas (North and South), production year and month. These data show that except for a slight decrease of limonene and an increase of some other monoterpenes such as sabinene and β-pinene, the oil compositions do not show much variation during the production season, while the oils obtained from fruits growing in the South have a higher content of oxygenated compounds than those growing in the North. This difference is in good agreement with the better olfactive properties of the South oils. The quantitative composition of the Italian oils is more similar to Uruguayan South oils than to the North ones.