This study aims at comparing GHG emissions and non-renewable energy use in meat sheep production, in organic farming (OF) and conventional farming systems. These two criteria have been calculated ex-post on 1261 French year-farms monitored over 26 years. The functional unit used is t he carcass weight. Regarding GHG emissions, the results show that OF emit 5 % less GHG than conventional ones, with a higher proportion of methane and less indirect CO2 associated to less inputs use. Given the methodological d difficulties, it is hard to argue if carbon sequestration in soil is different between OF and conventional. For non-renewable energy, there is no significant difference between OF and conventional farms, due to compensations (more mechanization and less concentrates and fertilizer purchased in OF). Note the great variability in the results, both in OF and conventional farms. The two main explanatory factors are ewe productivity (for GHG) and forage self-sufficiency (energy consumption).