Gevuina avellana Mol. oil have been valued for its nutritional and pharmacological properties. However, there is no knowledge about the process of oil formation in relation to kernel development and temperature. In Valdivia, Chile, and during two years, nut samples of G. avellana were collected from selected trees. ANOVAs tests and correlation analysis were conducted to assess changes in oil content and fatty acids profile in regard to sum of growing degree days. Oil percentage increased until the sum of 631 +/- 41 growing degree days, when 70% of kernel dry weight was reached. Monounsaturated fatty acids increased during kernel development, contrary to what occurred for polyunsaturated and saturated acids, with a final unsaturated: saturated ratio of 15.6: 1. Relative content of oleic and linoleic acids were significantly and negatively correlated (r(s)=-0.698; P<0.05). Percentage of C16: 1 Delta(11) acid was ever high, although it significantly (P<0.05) decreased during early stages of kernel growth. A significant and negative correlation was found between C16: 1.11 and the sum of unidentified C18: 1, C20: 1 and C22: 1 isomers. Fatty acids profile of G. avellana oil was stabilized between 772 +/- 21 to 888 +/- 3 growing degree days, when 85% of kernel dry weight was reached. Results are useful to establish orchards in optimal environmental an management conditions in order to maximize the production and quality of G. avellana oil.