Okla. Admin. Code § 710:65-1-10
Any item purchased for use or consumption by the purchaser is subject to sales or use tax at the time of purchase, even though the item may be resold later in either its original or altered form. Any exempt purchase is taxable in full at the time the purchaser first uses the item for a nonexempt purpose. For example, a rental company purchases a tractor exempt from sales tax for the purpose of renting the tractor to another person. If the rental company at some point determines it will withdraw the tractor from its inventory of items held for rental, and instead, will use the tractor for its own use in providing services, the "sales value" of the tractor is taxable at that point. The rental company must report the "sales value" of the tractor as a withdrawal from inventory on Line Two (2) of the sales tax report filed for the period when the determination was made and remit the applicable sales tax.
Okla. Admin. Code § 710:65-1-10