The term 'fermentable metabolisable energy' (AFRC, 1992) has been criticised as an index of the supply of fermentable energy to the rumen because it has not been measured directly, is insensitive to rumen outflow rate and assumes fermentation of some nutrients which bypass the rumen (Newbold, 1994). One alternative is to describe the content of fermentable energy in terms of the amount of gas evolved during fermentation by ruminal microorganisms. The automated pressure transducer technique of Davies et al. (1995) has been applied to individual concentrate feedstuffs to provide an alternative database of fermentable energy content (Baughan et al., unpublished).