Solubility data is essential for any application of supercritical fluids. A new technique has been developed using a piezoelectric quartz crystal to measure solubilities. A small mass-of solute is deposited on the crystal and solubility is measured by observing the crystal's frequency change as this solute dissolves in the supercritical fluid. The technique is ideally suited to solutes which exhibit low solubilities. Solubility measurements of bis(acetylacetonato)copper(II) (Cu(acac)(2)) in supercritical carbon dioxide were in good agreement with existing literature values. New solubility data were also measured for bis(thenoyltrifluoroacetonato)copper(II) (Cu(tta)(2)).