Agriculture is one of the major sources of methane in the UK and the major contribution is that from the ruminant animal. Most current inventories include evaluations of emission rates determined from ammals in respiration chambers. Methodolgy has been developed at IGER, North Wyke which enables measurements to be made with grazing animals (tunnel system). Preliminary measurements have indicated that methane emissions from grazing sheep in the tunnel system were lower than reported values for zero-grazed grass determined in chambers. The objective was to determine if these observed differences were a result of methodological differences.