Several theories have been proposed concerning the stand oil reaction but no precise reaction scheme has been described. In this work, the stand reaction of linseed oil was characterized in order to determine the nature of the products formed during this reaction. Using complementary analytical techniques (more especially NMR and mass spectrometry), the existence of two different reactions was demonstrated: the Diels-Alder addition between fatty acid chains and the addition of a methylene radical on double bonds, followed by combination or elimination reactions.