| #591 | Oesterreichisches Ingenieur-Archiv. -- Wien : Springer, 1946-1964. -- ISSN 0369-7819 |
| #592 | Operational research quarterly. -- Oxford : Pergamon Press, 1970-1977. -- ISSN 0030-3623 |
| #593 | Operations research. -- Baltimore : The Operations Research Society of America, 1956-. -- ISSN 0030-364X print. -- ISSN 1526-5463 online |
| #594 | Operations research letters. -- Amsterdam : North-Holland, 1981-. -- ISSN 0167-6377 print. -- ISSN 1872-7468 online |
| #595 | Opsearch. -- Delhi : Operation Research society of India, 1964-. -- ISSN 0030-3887 print. -- ISSN 0975-0320 online |
| #596 | Optimization. -- Yverdon : Akademie-Verlag, 1977-. -- ISSN 0233-1934 |
| #597 | Osaka Journal of Mathematics. -- Osaka : Osaka University, Department of Mathematics, 1964-. -- ISSN 0030-6126 |
| #598 | Osaka mathematical journal. -- Osaka : Osaka University. Faculty of Science. Department of Mathematics, 1949-1963. -- ISSN 0388-0699 |
| #599 | Pacific journal of mathematics. -- Berkeley : Pacific Journal of Mathematics, 1951-. -- ISSN 0030-8730 print. -- ISSN 1945-5844 online |
| #600 | Periodica mathematica Hungarica. -- Budapest : Kluwer Academic Publishers, 1971-. -- ISSN 0031-5303 print. -- ISSN 1588-2829 online |