Switchgrass (Panicum virgatum L.) is being evaluated as a cellulosic bioenergy crop. This study assessed the net energy efficiency and economic feasibility of switchgrass and similar crops. Field trials were conducted on 10 farms across the midcontinental U.S. to determine net energy and economic costs based on known farm inputs and harvested yields. Annual biomass yields of established fields averaged 5.2–11.1 Mg·ha⁻¹, resulting in an average estimated net energy yield (NEY) of 60 GJ·ha⁻¹·y⁻¹. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomass yield and an equivalent estimated NEY than previous estimates from human-made prairies that received low agricultural inputs. Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline. This study represents the genetic material and agronomic technology available for switchgrass production in 2000 and 2001. Improved genetics and agronomics may further enhance energy sustainability and biofuel yield of switchgrass. Switchgrass is a renewable biofuel source that can reduce reliance on fossil fuels, reduce GHG emissions, and enhance rural economies. Ethanol is the most common biofuel in the U.S. and is projected to increase in the short term due to the voluntary elimination of methyl tertiary butyl ether in conventional gasoline and in the long term due to U.S. government mandates. Maize or corn grain and other cereals such as sorghum are the primary feedstock for U.S. ethanol production, but competing feed and food demands on grain supplies and prices will eventually limit expansion of grain-ethanol capacity. An additional feedstock source for producing ethanol is the lignocellulosic components of plant biomass, from which ethanol can be produced via saccharification and fermentation. Dedicated perennial energy crops such as switchgrass, crop residues, and forestry biomass are major cellulosic ethanol sources that could potentially displace 30% of our current petroleum consumption. Net energy production has been used to evaluate the energy efficiency of ethanol derived from both grain and cellulosic biomass. Studies have used net energy values (NEV), net energy ratios, and net energy yield (NEY) and have compared biofuel output to petroleum requirements [petroleum energy ratio (PER)] to measure the sustainability of a biofuel. Switchgrass was estimated to have a net energy balance of 343% when used to produce biomass ethanol. More recent energy model analyses indicate that switchgrass could produce >700% more output than input energy. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomassSwitchgrass (Panicum virgatum L.) is being evaluated as a cellulosic bioenergy crop. This study assessed the net energy efficiency and economic feasibility of switchgrass and similar crops. Field trials were conducted on 10 farms across the midcontinental U.S. to determine net energy and economic costs based on known farm inputs and harvested yields. Annual biomass yields of established fields averaged 5.2–11.1 Mg·ha⁻¹, resulting in an average estimated net energy yield (NEY) of 60 GJ·ha⁻¹·y⁻¹. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomass yield and an equivalent estimated NEY than previous estimates from human-made prairies that received low agricultural inputs. Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline. This study represents the genetic material and agronomic technology available for switchgrass production in 2000 and 2001. Improved genetics and agronomics may further enhance energy sustainability and biofuel yield of switchgrass. Switchgrass is a renewable biofuel source that can reduce reliance on fossil fuels, reduce GHG emissions, and enhance rural economies. Ethanol is the most common biofuel in the U.S. and is projected to increase in the short term due to the voluntary elimination of methyl tertiary butyl ether in conventional gasoline and in the long term due to U.S. government mandates. Maize or corn grain and other cereals such as sorghum are the primary feedstock for U.S. ethanol production, but competing feed and food demands on grain supplies and prices will eventually limit expansion of grain-ethanol capacity. An additional feedstock source for producing ethanol is the lignocellulosic components of plant biomass, from which ethanol can be produced via saccharification and fermentation. Dedicated perennial energy crops such as switchgrass, crop residues, and forestry biomass are major cellulosic ethanol sources that could potentially displace 30% of our current petroleum consumption. Net energy production has been used to evaluate the energy efficiency of ethanol derived from both grain and cellulosic biomass. Studies have used net energy values (NEV), net energy ratios, and net energy yield (NEY) and have compared biofuel output to petroleum requirements [petroleum energy ratio (PER)] to measure the sustainability of a biofuel. Switchgrass was estimated to have a net energy balance of 343% when used to produce biomass ethanol. More recent energy model analyses indicate that switchgrass could produce >700% more output than input energy. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass monocultures managed for high yield produced 93% more biomass