A theoretical model of classical mechanical atom-surface scattering which includes both single and double collisions from a many-body target is applied to the determination of surface composition of molten metal alloys by rare gas scattering. Explicit calculations are compared with recently measured data for the scattering of monoenergetic beams of Ar atoms from the surface of liquid Ga-Bi alloys. These calculations indicate that rare gas scattering can provide a precise measure of surface segregation in the outermost layer of dilute liquid alloys. (C) 2003 American Institute of Physics.