Okla. Stat. tit. 12 § 178
Where the action is against two or more defendants, and one or more shall have been served, but not all of them, the plaintiff may proceed as follows:
First. If the action be against defendants jointly indebted upon contract, tort, or any other cause of action, he may proceed against the defendants served, unless the court otherwise direct; and if he recover judgment, it may be entered against all the defendants thus jointly indebted, so far only as that it may be enforced against the joint property of all, and the separate property of the defendants served; and if they are subject to arrest, against the persons of the defendants served.
Second. If the action be against defendants severally liable, he may, without prejudice to his rights against those not served, proceed against the defendants served in the same manner as if they were the only defendants.
Okla. Stat. tit. 12, § 178