Okla. Stat. tit. 12, § 12-182: Unincorporated associations and trusts - Suits against -

Service of process.

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.