A process for olefin oligomerization can include: contacting a feedstock comprising at least one C3 to C20 olefin/paraffin under oligomerization conditions in the presence of a Si/Al ZSM-23 catalyst having no amine treatment and a Si/Al2 molar ratio of 20 to 60 and/or a Si/Al/Ti ZSM-23 catalyst having no amine treatment, a Si/Al2 molar ratio of 20 to 60, and a Ti/Al molar ratio of 0.1 to 3; and recovering an oligomeric product comprising dimers having a branching index of less than 2.1, trimers having a branching index of less than 2.1, and tetramers having a branching index of less than 2.1.