Swarms of hybrids between cultivated rice and its weeds have been known in Taiwan, Thailand, China and India since the 1920's and appear now to be resident in the state of Arkansas. The USDA is currently funding work to evaluate the rate of pollen movement out of cultivars and into weeds, largely because of its interest in commercializing genetically modified rice. Greenhouse and limited field trials will determine, to some extent, the movement of cultivated genes into naturalized populations, but will provide only a snapshot of their history. Here we propose an approach to investigate the competitive dynamics and degrees of introgression between cultivated and weedy rice to assess the movement of transgenes in cultivation. Competition experiments provide a measure of population growth parameters for rice and red rice, as well as an indication of the commercial impact of transgenic-weed hybrids on rice production. Further, sampling genetic variation in hybrid swarms will provide an integrated, historical assessment of the movement of cultivated genes into weedy rice populations. The results of this work will assist in making decisions regarding the locations, and likely safe cultivars to consider for release as genetically modified organisms.