Okla. Stat. tit. 4, § 4-503: Carbon monoxide - Administration

Personnel shall be thoroughly instructed and be adequately

trained in the operation and use of the carbon monoxide chamber.

Carbon monoxide shall be administered in the following manner:

Adult animals, over sixteen (16) weeks of age, to be euthanized,

shall be left in the chamber for a minimum of twenty (20) minutes

after the carbon monoxide is administered. No animal so euthanized

shall be removed until five (5) minutes after cessation of

respiratory movements. The animal's body shall not be disposed of

until death has been confirmed.