ABSTRACT.- Understanding key animal performance and nuisance factors associated with methane (CH4) output and feed intake is crucial in developing greenhouse gas mitigation strategies and incorporating these traits into international sheep breeding goals. The objectives of the current study were to: 1) investigate animal and nuisance (environmental + management) factors associated with CH4 output and feed intake; and 2) determine relationships between CH4 output and feed efficiency in sheep and whether or not they differ by country. Methane output was measured in sheep in Ireland, Norway, New Zealand (NZ) and Uruguay using portable accumulation chambers (PAC), and in France using GreenFeed technology. Individual feed intake was quantified using various techniques across six countries (Ireland, United Kingdom, Norway, France, Uruguay, NZ), on sheep housed indoors, grazing outdoors, and consuming forage or a total mixed ration. Studies varied by sheep breed and age, as well as feed types and measurement methods; factors associated with the variability in CH4 output and feed intake therefore differed by country.