You can use OLTPRO to set up a direct debit when filing the Oklahoma state return.
Here are more options for taxpayers to pay their Oklahoma taxes:
Mail:
Individual Income Tax Form 511-V.. If you have already filed your current year's individual income tax return, and are now wanting to send in your payment due for your Individual Taxes you must include the 511-V voucher with your payment.511-V Voucher Oklahoma Tax Commission Post Office Box 26890 Oklahoma City, OK 73126-0890
Credit cards
https://oktap.tax.ok.gov/Oktap/Web/_/#1
Electronic Funds Transfer System (EFT)/E-Check
http://www.ok.gov/tax/Individuals/Income_Tax/E-File_Options/Payments_Options/Electronic_Funds_Transfer.html