Technical Abstract: Determining the life cycle greenhouse gas benefits of biofuels has been critical for quantifying their potential for meeting governmental mitigation targets. Little work has been conducted to determine the life cycle greenhouse gas benefits of using biomass for heat or power generation, even though this pathway, like ethanol, could also lead to reduced oil imports. The objective of this study was to quantify energy use from switchgrass seed to biomass production and quantify the net life cycle greenhouse gas emissions of densifying the biomass as pellets, cubes, and briquettes. Each phase of biofuel production differs in which sources of greenhouse gases dominate the analysis. We found that mitigating for prior land use history and removing plant species previously occupying the field (e.g. row crops, pasture) was a significant source of greenhouse gas emissions during both seed production and switchgrass establishment for biomass production. During switchgrass production, soil nitrous oxide emissions became the most import source of greenhouse gases. However the dominate factors affecting the quantity of greenhouse gas emissions associated with the final product were switchgrass harvest season and the type of densified product. When replacing heating oil, switchgrass offset at least 40% more oil than conversion to ethanol.