Different crystal growth methods were used to obtain single crystals of interstitial phases based on the α-boron structure in the B-O and B-C-O systems at pressures of 3-7 GPa and temperatures of 1500-2000 K. Boron suboxide carbide B(C,O) 0 . 1 6 crystals with sizes up to 250 μm, suitable for complete structure analysis, were prepared by chemical reaction between B 4 C and B 2 O 3 (molar ratio 1:1). The hexagonal unit cell parameters of the B(C,O) 0 . 1 6 compound are: a=5.618(1) Å, c=12.122(1) Å, c/a=2.158, Z=38.54 and space group R3m. The analytical method for estimation of the chemical composition and the number of atoms per unit cell is presented for this kind of compound.