Warm-season grasses in the Miscanthus genus have risen to the top of the list of candidates for bioenergy crop production in Illinois. Because plant species being considered as biofeedstocks share key traits with invasive species, there is concern they will escape cultivation and become noxious weeds. To evaluate this potential, we are conducting a quantitative risk assessment focused on Miscanthus x giganteus and Miscanthus sinensis. Our work consists of field research in both agricultural and nonagricultural environments as well as simulation models that pull all the information together to make predictions about invasion risk. Preliminary results suggest that the vegetative "Illinois clone" of Miscanthus x giganteus poses little invasion risk under typical conditions for crop production in central Illinois, whereas seeded Miscanthus species such as Miscanthus sinensis have greater invasion potential.