Excerpted from the 2000 Report of the AVMA Panel on Euthanasia –

Inhalant anesthetics

"With inhalant anesthetics, the animal can be placed in a closed receptacle …[and] the anesthetic can be introduced from a vaporizer. The latter method may be associated with a longer induction time. Vapors are inhaled until respiration ceases and death ensues. Because the liquid state of most inhalant anesthetics is irritating, animals should be exposed only to vapors. Also, sufficient air or O₂ must be provided during the induction period to prevent hypoxemia.

"In order of preference, halothane, enflurane, isoflurane, sevoflurane, methoxyflurane, and desflurane, with or without nitrous oxide, are acceptable for euthanasia of [rodents]."