Fossil fuel-derived inputs can increase cow-calf production per unit of land or labor but can raise financial and environmental concerns. Eleven US cow-calf systems from nine ecological regions in Iowa, South Dakota, Tennessee, and Texas were analyzed to determine quantities of energy used and carbon (C) emitted due to fossil fuel use (excluding emissions from soils and biota) and to determine how management and environment influenced those quantities. Total energy and C cost, calculated cow⁻¹ or ha⁻¹, were highly correlated (0.99). Energy use cow⁻¹ and ha⁻¹ varied greatly across systems, ranging from 3 000 to 12 600 megajoules (MJ) · cow⁻¹ · yr⁻¹ and from 260 to 20 800 MJ · ha⁻¹ · yr⁻¹. As stocking rate increased, MJ · cow⁻¹ increased at an increasing rate. Differences in quantity of fertilizer accounted for most variation in energy use. Fertilizer allowed higher stocking rates but reduced energy efficiency of liveweight marketed. Compared to intensive, higher stocking rate systems, rangeland systems based on native or naturalized forages used little or no fertilizer, but used more energy cow⁻¹ for crude protein (CP) supplementation, fencing, and pickup trucks. Across all systems, energy used to produce winter feed ranged from 0% to 46% of total energy. Northern systems used higher percentages of total energy for winter feed and fed for more days year⁻¹, but southern systems that included large amounts of bermudagrass (Cynodon dactylon L.) hay used the most MJ · cow⁻¹ for winter feed. Systems with high MJ · cow⁻¹ were vulnerable to shocks in energy prices. Reducing energy use and C emissions from cow-calf operations is possible, especially by reducing fertilizer and hay use, but would likely reduce productivity ha⁻¹. Forages with high nitrogen use efficiency, locally adapted plants and animals, and replacement of hay with unfertilized dormant forage and CP supplementation could reduce energy use.