A gradient method to determine directly and quantitatively ternary phase diagrams is reported. The gradients are created in standard X-ray capillaries. C-14 labeling and X-ray transmission measurements are used together in situ to obtain the exact sample composition along the gradient. Structural phase identification is obtained from SAXS analysis. Using this method, two cationic surfactant/glycolipid/water ternary systems have been investigated at different temperatures.