Oklahoma Taxes on non oklahoma oil and gas income

No, it is not taxable by Oklahoma.  It would be included in your federal income, which is the starting point for your Oklahoma tax return.  Some Out-of-State income is then subtracted on line 4 of Form 511.  Below is the description of out-of state income that is not taxed, according to the Oklahoma Tax Commission instructions for Form 511:

This is income from real or tangible personal property or business income in another state. This includes partnership gains and gains sustained by S corporations attributable to other states. It is not non-business interest or dividends, installment sale interest, salary/wages, pensions, unemployment compensation, gambling or income from personal services. (See instructions for line 16.) Provide a brief description of the type of out-of-state income deducted. Provide detailed schedule showing the type, nature and source of the income and copy of federal return. Documents submitted should reflect to which state(s) the income is attributable. Provide the other state’s return and/or Schedule K-1, if applicable.