Okla. Stat. tit. 68, § 68-2802.2: Date of delivery or payment

A. For any return, claim, statement, or other document required

to be filed with a county assessor in this state or any payment

required to be made to a county assessor in this state within a

prescribed period or on or before a prescribed date under authority

of the Ad Valorem Tax Code, the date of the postmark stamped on the

cover in which the return, claim, statement, or other document or

payment is mailed shall be deemed to be the date of delivery or the

date of payment, as the case may be.

B. The provisions of this section shall apply only if:

1. The postmark date falls within the prescribed period or on

or before the prescribed date for filing, including any extension,

of the return, claim, statement, or other document or for making

payment, including any extension granted for making such payment;

and

2. The return, claim, statement, or other document or payment

was, within the prescribed period or on or before the prescribed

date for filing, deposited in the mail in the United States in an

envelope or other appropriate wrapper, postage prepaid, properly

addressed to the county assessor with which the return, claim,

statement, or other document is required to be filed, or to which

the payment is required to be made.

C. For purposes of this section, if any return, claim,

statement, or other document or payment is sent by United States

registered mail, the registration shall be prima facie evidence that

the return, claim, statement, or other document or payment was

delivered to the county assessor to which addressed, and the date of

registration shall be deemed the postmark date.

D. The provisions of this section shall not apply with respect

to returns, claims, statements or other documents or payments which

are required under any provision of the Ad Valorem Tax Code to be

delivered by any method other than by mailing.

E. For the purposes of this section, if the prescribed period

ends on or the prescribed date is a legal holiday as defined by

Section 82.1 of Title 25 of the Oklahoma Statutes or any other day

when the office of the county assessor does not remain open for

public business until the regularly scheduled closing time, then the

prescribed period or prescribed date shall be extended until the end

of the next day upon which the office of the county assessor is open

for public business until the regularly scheduled closing time.