The Cu-C and Al-Cu-C phase diagrams were determined at 1550 °C to 2300 °C by chemical and X-ray diffraction analyses of alloys saturated with carbon within sealed graphite crucibles. Isothermal sections for the ternary system were determined at intervals of 150 °C over the range of temperatures investigated. The univariant points in atomic percent on the 1700 °C, 1850 °C, and 2000 °C isotherms are 70.7Al-28.9Cu-0.4C, 74.4Al-24.0Cu-1.6C, and 78.3Al-17.0Cu-4.7C, respectively, as determined by metallographic examination of rapidly cooled alloys. Graphite and Al4C3 (decomposition temperature 2156 °C) were the only solid phases observed at these temperatures. The excess partial Gibbs energy for dissolved carbon in the liquid Al-Cu-C solutions in equilibrium with C, as calculated from the experimental solubilities, is¯ Gce = - RT lnx =y2[176,860 - 55.42T - (224,200 - 110.84T)x] +z2[237,000 - 48.61T] +yz[320,510 - 36.77T + (30,180 + 35.10T)z + (51,570 - 74.13T)yz + (246,400 - 88.04T)yz2 - 60,000], J/g atom where R is the gas constant,T is the temperature in K, andx, y, andz are the atomic fractions of C, Al, and Cu, respectively. The equation also is a good approximation for liquid solutions in equilibrium with A14C3.