The main disadvantages of the rumen fluid in vitro technique are the cost and welfare issues of keeping cannulated animals. The purpose of the study was to find an accurate alternative in vitro technique to determine organic matter digestibility (OMD) of Atriplex nummularia supplemented with two energy sources. The in vitro faeces technique of El Shaer et al. (1987) is an easier and cheaper alternative to the classic rumen fluid in vitro technique of Tilley & Terry (1963), as modified by Engels & Van der Merwe (1967). The in vitro gas production technique of Piennaar (1994), the cellulase in vitro techniques of De Boever et al. (1986) and the modified Wageningen one, were not as accurate determining OMD as the in vivo technique.