Okla. Stat. tit. 68, § 68-2381: Applicability of act to taxable years

The provisions of this act shall apply to all taxpayers whose

taxable year begins on and after January 1, 1971; provided, however,

that in respect to any taxpayer whose taxable year begins in 1970

and ends in 1971, such taxpayer may, at his option, determine his

tax under this act or compute his tax liability for such fiscal year

ending in 1971, by using the sum of the computations of 1, and 2, as

follows:

1. The tax computed under the provisions of the law applicable

to the calendar year 1970, multiplied by the ratio of the number of

months of the year in 1970, to the total number of months of the

taxable year.

2. The tax computed under the provisions of this law applicable

to the calendar year 1971, multiplied by the ratio of the number of

months of the year in 1971, to the total number of months of the

taxable year.