Limited information is available regarding the effect of common management practices on the energy balance of corn and soybean cropping systems. Energy balances were calculated for continuous corn, continuous soybean, and corn-soybean rotations under six tillage treatments that included no-tillage, chisel plow, tandom disk, subsoiling, ridge till, and moldboard plow. Calculations were based on a trial conducted on a silty clay loam soil near Lincoln, NE from 1986 to 2001. Inputs for the calculations included energy required to produce fertilizer and pesticide, fuel required for field operations, and energy required to manufacture equipment. Outputs were the energy contained in the harvested grain. Energy balances were evaluated in terms of yield (mg/ha), energy input (GJ/ha), energy output (GJ/ha), energy gain (GJ/ha), energy intensity (MJ/grain equivalent), and output/input ratio. Lowest energy inputs were required for no-tillage soybean and highest for corn under plow tillage. Energy efficiency was effected strongly by crop and crop rotation but only slightly by tillage treatment.