Fermentable energy (FE) was defined in the latest United Kingdom metabolizable protein system as energy available for microbial protein growth and multiplication in the rumen (Agricultural and Food Research Council, 1992). In this system the FE value was calculated by subtracting the metabolizable energy (ME) of fat and ME of any fermentation products from the ME of the food. This estimation is indirect and largely based on whole tract digestion data, thus it can not take into account the influence of rumen outflow, fermentation and degradation rate and digesta retention time in the rumen. In addition, this approach does not take into account undegradable protein and /or starch. As a result, the precision of the FE values are questionable. Therefore a precise, accurate, rapid, cheap and direct technique to measure FE from food ingredients should be developed. Such a technique should consider the factors mentioned above. This work evaluated the ability of four techniques to estimate the FE value of concentrate foods for ruminants.