Concerns about genetically engineered crop plants center on three conjectural risks: that transgenic crop plants will become weeds of agriculture or invasive of natural habitats; that their engineered genes will be transferred by pollen to wild relatives whose hybrid offspring will then become more weedy or more invasive; or that the engineered plants will be a direct hazard to humans, domestic animals or beneficial wild organisms (toxic or tocal for assessing the invasiveness of plants. The object is to determine whether genetic engineering for herbicide tolerance affects the likelihood of oilseed rape becoming invasive of natural habitats. By estimating the demographic parameters of transgenic and conventional oilseed rape growing in a variety of habitats and under a range of climatic conditions, we obtain and direct comparison of the ecological performance of three different genetic lines (control, kanamycin tolerant transgenics and herbicide tolerant transgenic lines). Despite substantial variation in seed survival, plant growth and seed production between production between sites and across experimental treatments, there was no indication that genetic engineering for kanomycin tolerance or herbicide tolerance increased the invasive potential of oilseed rape. In those cases in which there were significant differences (such as seed survival on burial), transgenic lines were less invasive and less persistent than their conventional counterparts.