Tree leaves are important fodders in many less developed countries, particularly in dry seasons when alternative feeds can be scarce. Although many leaves appear to be good quality fodders due to their generally high crude protein content, many contain anti-nutritive factors which reduce their nutritive value. Tannins are the most widespread of the anti-nutritive factors and are to be found in many tree species. An in vitro gas production method has been developed by Theodorou et al (1994) and applied to the ranking of tree leaf fodders (Wood et al, 1993). This paper combines data obtained from three separate pieces of work investigating the nutritive value of tree leaf fodders in Bolivia, West Africa and Colombia. It seeks to investigate relationships between in vitro gas production at various times of incubation and proximate composition, fibre and tannin content in order to identify which components are of particular importance in determining gas production characteristics and whether these relationships are consistent over a wide range of species from different sources.