| Oddball Draw | Five down; Lead bet; Draw three, four with an ace; Lead bet; Buy one; Lead bet; Showdown |
| Oedipus | Seven down; Pass three left; Pass two left; Pass one left; Discard two; Put cards in order; Flip the top one; High bet; Flip the top one; High bet; Flip the top one; High bet; Flip the top one; High bet; High/low declare |
| Ohio | Five down; Five common down; Flip one common card; Lead bet; Flip one common card; Lead bet; Flip one common card; Lead bet; Flip one common card; Lead bet; Flip one common card; Lead bet; High/low/both declare; Low common indicates wild |
| Oklahoma | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; Showdown; Use exactly two down cards; The last common, a die roll, and the difference are wild |
| Oklahoma Lowball | One down; One up; High bet; One up; High bet; One up; High bet; One up; High bet; Casino lowball |
| Oklahoma Sold'em | Two down; Twist two; Lead bet; Three common up; Twist two; Lead bet; Twist one; Lead bet if anyone twisted; One common up; Lead bet; One common up; Lead bet; Showdown |
| Old English Draw | Five down; Lead bet with two blinds and a straddle; Draw three, four with an ace; Lead bet; Showdown, high with cats and dogs |
| Old West | One down; One up; High bet; One up; High bet; One up; High bet; One up; High bet; Twist one; High bet; High/low declare |
| Omaha 33 | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; Pay to change card restriction; Coin in hand high/low/both; Lead bet; High/low/both |
| Omaha 8's | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; High/low/both cards speak; Use exactly two down cards; Eight low qualifier |
| Omaha Burns | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; Knock; One common up; Lead bet; High/low/both cards speak with burn; Use exactly two down cards |
| Omaha High/High | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; Showdown, high splits with second high; Use exactly two down cards |
| Omaha High/Low | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; High/low/both cards speak; Use exactly two down cards; Eight low qualifier |
| Omaha High/Low Make It | Five down; Discard one and reshuffle; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; High/low/both cards speak; Use exactly two down cards; Eight low qualifier |
| Omaha Hold'em | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; Showdown; Use exactly two down cards |
| Omaha Spade | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; High hand splits with low spade in the hole; Use exactly two down cards |
| Omaha, Nebraska | Four down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; Showdown; Use two or three down cards |
| Omahaholdemapple | Five down; Lead bet; Discard one; Three common up; Lead bet; Discard one; One common up; Lead bet; Discard one; One common up; Lead bet; Showdown |
| One Card Substitution | One down; One up; High bet; One up; High bet; One up; High bet; One up; High bet; Twist one; High bet; Showdown |
| One Eye Blind | Two down; Lead bet; Three common up; Lead bet; One common up; Lead bet; One common up; Lead bet; Take one from your left; Showdown |
| One Eyed King | Five down; Lead bet; Draw three, four with an ace; Lead bet; Showdown; One eyed king is wild |
| One Line Lebanese | Five down; Discard one and reshuffle; Lead bet; Three common up; Last raiser bets; One common up; Last raiser bets; One common up; Last raiser bets; High/low/both cards speak; Use exactly two down cards; Eight low qualifier |
| One Man's Trash | Two down; Lead bet; Five common up; Lead bet; The lead discards two commons; Two common up; Lead bet; Repeat once for each player; Showdown |
| One Red Card | Fifteen down; Flip any number; Best hand gets a point; Lead bet; Flip any number; Best hand gets a point; Lead bet; Flip any number; Best hand gets a point; Lead bet; Flip any number; Best hand gets a point; Lead bet; Flip any number; Best hand gets a point; Lead bet; Most points takes the pot |
| One Three One | One down; One up; High bet; One up; High bet; One up; High bet; One down; High bet; High/low declare |
| One Three One Replace | One down; One up; High bet; One up; High bet; One up; High bet; One down; High bet; Twist one; Lead bet; Twist one; Lead bet; High/low declare |
| One Two Three | Three down; Lead bet; Draw three; Lead bet; Draw two; Lead bet; Draw one; Lead bet; Closest to ace, two, three wins |
| Open Hand Kenosha | Two down; One up; Lead bet; One up; Lead bet; Repeat until someone thinks they've won; Lead bet; Showdown |
| Oppression | Seven down; Split cards into two hands; Coin in hand; Losers match the pot once; Reante; Discard the two card hand; Put cards in order; Lead bet; Flip the top one; High bet; Flip the top one; High bet; Flip the top one; High bet; Flip the top one; High bet; Showdown |
| Option Alley | One down; One up; High bet; One up; High bet; One up; High bet; One up; High bet; Twist one; High bet; High/low declare |
| Option and Twist | One down; One up; High bet; One up; High bet; One up; High bet; One up; High bet; One up, pay to get it down; High bet; Twist one; High bet; Showdown |
| Orbit | Five down; Eight commons down in a circle and one in the middle; Lead bet; Flip two opposite commons, going clockwise; Lead bet; Flip two opposite commons, going clockwise; Lead bet; Flip two opposite commons, going clockwise; Lead bet; Flip two opposite commons, going clockwise; Lead bet; Flip one common card; Showdown; Use three consecutive circle cards; Last common indicates wild |
| Orchids | Seven down; Pass three left; Discard two; Put cards in order; Flip the top one; High bet; Flip the top one; High bet; Flip the top one; High bet; Flip the top one; High bet; High/low declare |
| Out at Home | Three down; Four common down in a diamond; Flip first base; Lead bet; Flip the top common; Lead bet; Flip one going around widdershins; Lead bet; Flip one common card; Lead bet; Showdown; Common face cards force a redeal; Fours give everyone a card |
| Oxford Stud | Two down; One up; Low bet; Two common up; Low bet; One up; Low bet; One common up; Low bet; High/low declare |
| The Oppressed Get Even | Seven down; Split cards into two hands; Coin in hand; Losers match the pot once; Reante; Discard the two card hand and reshuffle; Lead bet; Draw three, four with an ace; Lead bet; Showdown; The winning two cards indicate wild |