The assessment of the likelihood of transgene spread from cultivated species to their wild relatives is relevant for oilseed rape (Brassica napus, AACC, 2n=38) as it is partially allogamous and presents numerous wild relatives growing nearby in cultivated areas and having an overlapping of the flowering period. We have assessed the probability of F1 interspecific hybrid formation between oilseed rape and three main weeds encountered in France, wild mustard (Sinapis arvensis, SarSar, 2n=18), hoary mustard (Hirschfeldia incana, AdAd, 2n=14) and wild radish (Raphanus raphanistrum, RrRr, 2n=18), under optimal conditions. Because of the higher frequency of interspecific hybrids observed with this latter weed, complementary field experiments were carried out under normal agronomic conditions. The F1 hybrids obtained showed different genomic structures, either 2n=28, or 2n=37, or 2n=56. These different hybrids were cultivated in the presence of wild radish and the succeeding generations were studied.