The production of fossil fuels will crest within the next decade and with reliance of modern conventional agriculture on fossil fuel energy inputs, food production will be stressed. Modern production practices also have negative impacts on the environment, but it is well established that the ecological impact of conventional agriculture can be reduced by utilizing alternative agricultural practices. Conservation tillage practices and diverse crop rotations reduce the need for fossil fuel energy inputs while maintaining high crop yields. An ongoing field experiment in the Central Corn Belt compares viable alternative systems to conventional corn-soybean rotations. The alternative systems, referred to as Low-External-Input (LEI) systems, incorporate diverse crop rotations (of 3 or 4 years) and alternative input sources with conventional techniques. The goal of the present study was to compare the energy use efficiencies of the LEI systems versus conventional agriculture. An energy analysis performed on 6 years of field log data from the experiment. The 3- and 4-year LEI systems reduced fossil fuel energy use by 41% and 56%, respectively, compared to the 2-year conventional system. The primary energy input for all rotations was grain drying. The monetary return, harvested weight, and potential energy of the 2-year and 4-year systems were similar. Efficiency ratios, calculated as a ratio between the outputs and input energy levels, were significantly improved in the LEI systems, with most of the variability due to differences in energy inputs. According to the output measurements selected, LEI systems are more energy efficient than conventional corn-soybean production systems, but the increased management time required in the LEI rotations coupled with high priced labor and cheap fossil fuels retards the adoption of these cropping systems.