Agriculture relies on fossil fuel inputs for production processes, but their use is also problematic because of fi nite supplies, release of associated CO 2 , and energy price fl uctuations. In the Texas High Plains, integrated crop-livestock systems were proposed to reduce soil erosion, N-fertilizer use, and reliance on the Ogallala aquifer, a source of irrigation water that is being rapidly depleted. We compared fossil fuel use and associated C emissions of an integrated crop-livestock system and a cotton (Gossypium hirsutum L.) monoculture system in a randomized block design evaluated for 10 yr. Energy use and C emissions ha -1 by the integrated system were less than the monoculture system when only one group yr -1 of beef stocker steers (Bos taurus) grazed the integrated system. When stocking rate increased, energy required by the integrated system rose due to additional cost required to support a larger off -site cow herd that provided stockers. Th e monoculture system used more energy than the integrated system for irrigation, fertilizer, pesticides, and mechanical operations. Energy effi ciency of producing cotton lint (25 MJ kg -1 ) was similar between the two systems. Th e integrated system's perennial grass WW-B. Dahl old world bluestem [Bothriochloa bladhii (Retz) S.T. Blake] was more effi cient at producing grazing days (32 MJ animal d -1 ) than the annuals wheat (Triticum aestivum L.) and rye (Secale cereale L.; 80 and 48 MJ animal d -1 , respectively). As the aquifer is depleted and water is pumped from greater depths, the integrated system's lower water use will save energy relative to the monoculture.