This study was conducted to determine the effects of atmospheric carbon dioxide concentration (CO₂) and air temperature on four Southern USA rice cultivars. In 2000, ‘Cocodrie’, ‘Cypress’ and ‘Jefferson’ were grown season-long in outdoor, naturally sunlit, controlled environment chambers in constant day/night air temperature regimes from 24 to 40℃ under an elevated CO₂. In 2002, the rice cultivar ‘Lamont’ was grown with day/night air temperature treatments of 19/15 to 35/31℃ under elevated CO₂. The CO₂ enrichment increased grain yield by 46 to 71% among the three cultivars in 2000. In 2002, CO₂ enrichment resulted in a non-significant increase in seed yield for the MC but more than doubled RC yields. We conclude that: i) these four USA rice cultivars may be more sensitive to high temperature stresses on reproductive development than some previously studied Asian rice cultivars; ii) the wide range in grain yield responses to CO₂ among these four cultivars points to the potential for breeding rice cultivars that are more responsive to expected future global levels of atmospheric CO₂ and; iii) elevated CO₂ may result in enhanced ratoon crop growth and yield.