Three species of Casuarina namely C. cunninghamiana, C. glauca and the natural hybrid C. cunninghamiana X C. glauca were evaluated for their biomass production and volume. Seedlings of these species were planted in the year 1982 at initial spacing of 1.5 X 2.5 m in an experimental species trial under irrigation with treated municipal effluent. The experiment took place at the Agricultural Research station of the college of Agriculture at Dirab near Riyadh, Saudi Arabia. During the following years, repetitive selective thinning was applied to the whole experiment. At theage of 16 years, three trees from each species were randomly chosen and felled down. Thedimensional parameters and biomass components of each tree were determined. The highest total above ground biomass ?TAGB? (400 kg tree-1), as well as the highest merchantable stem volume ?MV? (0.37 m3 tree-1) was recorded for C. cunninghamiana followed by C. glauca (200 kg tree-1 and 0.21 m3 tree-1) then the hybrid (175 kg tree-1 and 0.19 m3 tree-1). Mathematical relationshipswere established for the prediction of both TAGB and MV using some dimensional parameters (e.g. diameter at breast height, DBH; total height, TH and merchantable height, MH). The correlation coefficients of these relationships were highly significant but differed according to species.