Okla. Stat. tit. 68, § 68-2360: Accounting periods and methods

A. The taxpayer's taxable year under this act shall be the same

as his taxable year for federal income tax purposes. If, on the

effective date of this act, the taxpayer's taxable year for Oklahoma

income tax purposes is different than his taxable year for federal

income tax purposes, the taxpayer shall file a return for the short

period ending on the day for which his current taxable year for

federal income tax purposes ends. If such taxpayer's taxable year

for federal income tax purposes ends after his taxable year for

Oklahoma income tax purposes, then the taxpayer shall file a return

for such regular Oklahoma taxable year and a return for the short

period ending with the federal taxable year.

The Tax Commission shall prescribe and promulgate all necessary

rules and regulations for annualizing income and/or deductions for

short years necessitated by the transition, if any, to the federal

taxable year.

B. If a taxpayer's taxable year is changed for federal income

tax purposes, his Oklahoma taxable year shall be similarly changed

under the same rules applicable under the Internal Revenue Code.

C. The taxpayer's method of accounting under this act shall be

the same as his method of accounting for federal income tax

purposes.

D. If a taxpayer's method of accounting is changed for federal

income tax purposes, such taxpayer's method for Oklahoma income tax

purposes shall be similarly changed under the same rules applicable

under the Internal Revenue Code.