O
- Karen O (b. 1978) — Where the Wild Things Are, Jackass Number Two
- Richard O'Brien (b.1942) — Shock Treatment
- Martin O'Donnell (b. 1955) — Halo, Myth, Oni
- Tom O'Horgan
- Walter O'Keefe
- Sharon O'Neill
- Paul Oakenfold (b. 1963) — Swordfish, Appleseed, Vexille, Nobel Son
- Erkan Oğur (b. 1954) — The Bandit, Toss-Up
- Hisayoshi Ogura
- Mike Oldfield
- Orbital (formed 1989) — Event Horizon, Octane, Pusher
- Norman Orenstein — American Psycho 2, Diary of the Dead, Cube 2: Hypercube
- Shinji Orito
- Buxton Orr
- Riz Ortolani (b. 1931) — Cannibal Holocaust, Africa Addio, Mondo cane
- Michiru Oshima (b. 1961) — Ico, Legend of Legaia, Arc the Lad, Fullmetal Alchemist
- Osibisa (formed 1969) — Superfly T.N.T.
- Kow Otani (b. 1957) — Gamera: Guardian of the Universe, Shadow of the Colossus, Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack
- Alex Otterlei — Xyanide, Totems
- John Ottman (b.1964) — The Usual Suspects, Fantastic Four, Snow White: A Tale of Terror, I Have No Mouth, and I Must Scream, X2
- Vyacheslav Ovchinnikov (b.1936) — Ivan's Childhood, Andrei Rublev, War and Peace
- Mark Ovenden — Yolngu Boy
- Reg Owen (1921 - 1978) — Very Important Person, Payroll
- Atilla Özdemiroğlu (b. 1943) — Night Journey, Akrebin Yolculuğu
Read more about this topic: List Of Film Score Composers