[en] The principal energy source of a pre-Main-Sequence (PMS) star is gravitational contraction. Mass ejection, regardless of its actual mechanism, in effect transfers gravitational potential energy from the entire star to the escaping matter. The virial theorem limits the efficiency of such a process. Theoretical PMS mass-radius relationships limit the total loss to a few tenths of the initial mass. The observed luminosities and estimated mass loss rates of T-Tauri stars are used to estimate the fraction of available energy expended on mass ejection. Actual losses appear to be much smaller than the theoretical limit in most cases. Only stars of emission line intensity classes 4 and 5 may be capable of significant mass loss. (Auth.)