Ooze
Anthony M. Rud
Operation Afreet
Poul Anderson
Operation Chaos (1)
Operation Desert Fox
Mercedes Lackey & Larry Dixon
Bolo (1)
Operation Haystack
Frank Herbert
Operation High Time
Jacqueline Lichtenberg
Sime/Gen (13)
Operation Syndrome
The Operator
Christopher Anvil
Federation of Humanity (1)
Options
John Varley
Eight Worlds (1)
Or Battle's Sound
Harry Harrison
Matter Transmitter (1)
The Oracle and the Mountains
Stephen King
Roland (1)
Oracles
Robert Reed
The Orangery
K. D. Wentworth
The Orb of Probability
Nat Schachner
Origin of Species
Robert F. Young
Origin Story
Kelly Link
Original Sin
Vernor Vinge
Richard A. Lovett