The olive industry in Northwestern Argentina has experienced substantial growth during the past two decades to produce virgin olive oil for export. To assess the fatty acid profiles of the main varietal olive oils, 563 oil samples from 17 varieties cultivated in the province of La Rioja were analyzed from 2005-2008. Olive varieties were ranked according to oleic acid content as low (65%; Manzanilla, Empeltre, Leccino, Coratina, Changlot, Picual). Using data from this study and the literature, the fatty acid composition of Spanish (Arbequina, Picual) and Italian (Coratina, Frantoio) varieties indicated consistently lower oleic acid contents when grown in NW Argentina versus the Mediterranean. For Arbequina, the oleic content decreased with increasing temperature during oil accumulation (-2% per °C). The classification of varieties should be useful in the selection of virgin olive oils for corrective blending and for choosing varieties for new orchards in order to meet IOOC requirements. The differences in fatty acid composition between NW Argentina and the Mediterranean Basin are most likely to be related to a genotype produced by environmental interaction, and the negative effect of the high seasonal mean temperature during oil accumulation will need further research.