Technical Abstract: Global transportation demands have led to concerns about the sustainability, costs, and environmental consequences of relying on petroleum to meet future energy needs. Future low-carbon fuel standards (LCFS) are being implemented worldwide to evaluate alternative fuel potential in reducing greenhouse gas (GHG) emissions from current petroleum-based fuels. Biomass is seen as a potential energy source to meet future LCFS. Sustainability concerns with biomass crops have been about the net energy efficiency, potential GHG emissions, and overall economic feasibility. Dedicated herbaceous plants and agricultural residues are expected to supply substantial amounts of biomass for conversion into biofuels. Biomass supplies will be constrained by feedstock transportation cost, which may require the use of multi-feedstocks for a given region to adequately and reliably supply a biorefinery. The use of agricultural residues and dedicated energy crops for bioenergy each have advantages and disadvantages in regards to energy sustainability and GHG emissions. Agricultural residues are perceived to have lower economic feedstock costs than dedicated energy crops, a major factor for an emerging cellulosic biofuel industry. Excessive agricultural residue removal, however, can lead to increased soil erosion and decreased soil organic carbon while the use of dedicated energy crops on productive cropland may initiate indirect land use changes. The objective of this presentation is to evaluate the overall effectiveness of corn stover, wheat straw and switchgrass (Panicum virgatum L.) to mitigate GHG emissions, displace petroleum, and evaluate net energy yield. These potential cellulosic feedstocks will be compared with current corn grain ethanol and nonrenewable fuels in terms of GHG emissions. Agronomic practices and biorefinery technology will be analyzed in their ability to increase bioenergy efficiency and sustainability. The potential for soil carbon storage of perennial energy crops such as switchgrass, is large, with sequestration rates of 53 Mg CO2 ha-1 being found in a 5 yr on-farm study. Currently, direct and indirect soil carbon changes are not standardized within life-cycle models to ensure GHG emissions are accurately accounted for in perennial bioenergy systems. This lack of standardization between direct and indirect soil carbon changes for perennial bioenergy systems can result in substantial biofuel GHG emission overestimates by current life-cycle models. Evaluating a bioenergy feedstock strictly on GHG emissions may also result in feedstocks that do not substantially displace nonrenewable fuels in industrialized countries.