Books in Science Fiction (sorted alphabetically)
- Odyssey of Sam Meecham Charles E. Fritch
- Of All Possible Worlds William Tenn
- Off Course Mack Reynolds
- Off on a Comet Jules Verne
- Off on a Comet! a Journey through Planetary Space Jules Verne
- Of Time and Texas William F. Nolan
- Oh, Rats! Miriam Allen De Ford
- Old Friends Are the Best Jack Sharkey
- Old Mr. Wiley Greye La Spina
- Old Rambling House Frank Herbert
- Omega, the Man Lowell Howard Morrow
- Omnilingual H. Beam Piper
- On a Torn-Away World; Or, the Captives of the Great Earthquake Roy Rockwood
- Once a Greech Evelyn E. Smith
- One Against the Moon Donald A. Wollheim
- One and the Many Stephen Marlowe
- One Man's Poison Robert Sheckley
- One Martian Afternoon Tom Leahy
- Oneness James H. Schmitz
- One Out of Ten J. Anthony Ferlaine
- One-Shot James Blish
- One Way Miriam Allen De Ford
- On Handling the Data M. I. Mayfield
- Onslaught from Rigel Fletcher Pratt
- On the Fourth Planet Jesse F. Bone