We also do not require this. http://okcommerce.gov/wp-content/uploads/2015/06/Oklahoma_Business_Startup_Guide.pdf
The document from the OK Commerce Department indicates under "Registering a Business Name" that the owner "can" see to register it for exclusive use. They are encouraged to do so. I take this to mean that the State of Oklahoma does not require you to register a DBA.
Further down in that section, it also states " that many bankers will require sole proprietors to obtain a Certificate of Fictitious Name which identifies the person who is the sole owner of the business.
It appears to be an added burden that banks are placing on sole proprietorships.