Okla. Stat. tit. 68 § 400.4
In the event the tax imposed by this act is not paid by the wholesaler as provided in Section 3 of this act and must be collected as a backup tax from the retailer or consumer in accordance with Section 4 of this act, the tax is due and payable by the retailer or consumer on the first day of each month for the preceding calendar month, and if not paid on or before the twentieth day of the following month, shall be delinquent. The retailer or consumer shall file with the Oklahoma Tax Commission, on forms furnished by the Tax Commission, a return verified by affidavit showing in detail the total purchase price of the tobacco products, the location of the purchase of the tobacco products and any other information the Tax Commission may deem reasonably necessary. With each return, the retailer or consumer shall remit to the Tax Commission the amount of tax shown on the return to be due. Reports timely mailed shall be considered timely filed. If a report is not timely filed, interest shall be charged from the date the report should have been filed until the date the report is actually filed.
Okla. Stat. tit. 68, § 400.4