The Q-value dependence of the cross section of heavy-ion transfer reactions to high-lying states is studied. The continuum energy spectra are measured for each exit channel while systematically varying the bombarding energy, scattering angle, target and projectile: /sup 16/O+/sup 232/Th, /sup 15/N+/sup 232/Th and /sup 181/Ta, and /sup 35/Cl+/sup 181/Ta at energies ranging up to 1.4 times the Coulomb barrier, at and about the grazing angle. The transfer reactions exhibit common properties which depend mainly on the number of transferred nucleons ..delta..N. The average amount of energy dissipated, which depends strongly on ..delta..N, is interpreted with a semiclassical model that assumes momentum matching and the presence of a velocity-dependent frictional force. Also, the branching ratios of the exit channels are observed to depend systematically on ..delta..N, which suggests a statistical process. The energy spectra are examined in terms of a phenomenological constrained phase-space analysis. The dominant constraint is found to be the optimal Q value. The description of data with at most two constraints implies that essentially all of the information content of the energy distribution is contained in these constraints.