Okla. Stat. tit. 36, § 36-1617: Equipment trust certificates

An insurer may invest in equipment trust obligations or

certificates which in the opinion of the Insurance Commissioner are

adequately secured, or other instruments so secured and evidencing

an interest in transportation equipment, wholly or in part within

the United States, which carry the right to receive determined

portions of rental, purchase, or other fixed obligatory payments to

be made for the use or purchase of such transportation equipment.