Linear polarization measurements have been performed for γ rays in 91Ru produced with the 58Ni(36Ar, 2p1nγ)91Ru reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the γ-γ coincidences, γ-ray linear polarization, and γ-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3-1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in 91Ru. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2 + ) and (17/2 + ) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2 + ) and (17/2 + ) states in terms of the J max and J max -2 members of the seniority-three ν ( g 9 / 2 ) - 3 multiplet.