To determine K 0 of three Mo 2-x W x BC solid solutions (x= 0, 0.5, 0.75), synchrotron diffraction patterns were collected upon hydrostatic DAC compression. The diffraction data were evaluated using MAUD software, refining lattice parameters of both the borocarbides and internal platinum pressure calibrant to monitor pressure. Mo 2 BC, Mo 1.5 W 0.5 BC, and Mo 1.25 W 0.75 BC were compressed to ∼54 GPa, ∼55 GPa, and ∼60 GPa, respectively, as determined by the platinum EOS. Refined lattice parameters, associated error, and calculated pressure values are presented in Tables . Figure illustrates the diffraction data as an intensity map for each Mo 2-x W x BC solid solution, demonstrating compression of the crystal structure as peaks shift to higher Q-space values with increasing pressure. In all of the collected spectra, observed peaks could be indexed to either the orthorhombic borocarbide phase or to the platinum or ruby internal pressure calibrants, with no indication of phase transformations across the entire pressure range.