Olive Mountain Keelback 
Olive ridley sea turtle 
Olive Sand Snake 
Olive sea snake 
Olive Trapezoid Snake 
Olive tree skink 
Oliver's Parrot Snake 
Orange-collared keelback 
Orange-lipped Keelback 
Orange-sided Bar-lipped Skink 
Orange-winged Flying Lizard 
Oriental Garden Lizard 
Oriental Long-tailed Grass Lizard 
Oriental ratsnake 
Oriental Whipsnake 
Oriental wolf snake 
Orinoco crocodile 
Ornate 
Ornate Cat-eyed Snake 
Ornate flying snake 
Ornate Girdled Lizard 
Ornate Olympic Snake 
Ornate Snail-eating Snake 
Ornate tree lizard