Agriculture relies on fossil fuel inputs for production processes but their use is also problematic because of finite supplies release of associated CO2 and energy price fluctuations. 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. The monoculture system used more energy than the integrated system for irrigation fertilizer pesticides and mechanical operations. Energy efficiency of producing cotton lint (25 MJ kg-1) was similar between the two systems. The integrated system's perennial grass WW-B. Dahl old world bluestem [Bothriochloa bladhii (Retz) S.T. Blake] was more efficient 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.