Okla. Stat. tit. 12 § 182
When any two or more persons associate themselves together and transact business for gain or speculation under a particular appellation, not being incorporated, they may be sued by such appellation without naming the individuals composing such association and service of process may be had upon such association by personal service as provided by law for services of summons in civil actions, upon any member of such unincorporated association, or, if the case be one in which service by publication may be had under the laws of this state, and service of summons either within or outside of the state cannot be had, with due diligence, upon any of the members of such unincorporated association, service by publication may be had upon such association by its particular appellation. Provided further, that service may be had upon any common law trust or any other unincorporated association or trust of individuals designating themselves as a trust or represented by an individual as trustee, by service upon any one of such individuals as may be designated as trustee for said trust, the same as in any other civil action. Venue in such cases, in addition to that now provided, shall be the same as that provided for actions involving domestic corporations.
Okla. Stat. tit. 12, § 182