Omaha High vs. Omaha Hi-Lo

Conveniently for those who know Omaha High, Omaha Hi-Lo is played according to almost identical rules.
The only time the High and Hi-Lo differ rules-wise is at the showdown.
Omaha Hi-Lo, also known as Omaha High-Low, O8 and Omaha 8-or-Better, is one of the most popular and entertaining forms of poker in the world.
Because this article only details the differences between Omaha High and Omaha Hi-Lo, if you aren't familiar with the rules and game play of Omaha High, you're going to want to read this article:

• Omaha Poker Rules and Game Play

Assuming you understand how to play marked cards Omaha High, let's look at what distinguishes the two games.

Omaha Hi-Lo Showdown Rules

Omaha Hi-Lo is a "split pot" game, meaning that at showdown, the pot is divided in half, with one half being awarded to the winning best hand, and the other half to the best qualifying "low hand."

The High

The winning high hand in Omaha Hi-Lo is identical to that of Omaha High. There are no qualification requirements for the high, meaning there will always be a winning high hand.

• Poker Hand Ranking
  

The Low

Low hands must qualify to be eligible for winning the low half of the pot.

• A low hand is composed of any two cards from a player's hand, and any three cards from the board (community cards).
• The cards a player uses for his best High hand have no effect on the low. The player can use the same cards, different ones or a combination from his hand.
• A qualifying low hand is defined as five unpaired cards, all with ranks at or below 8.
• Aces are considered low for the low hand.
• Flushes and straights are ignored for the low, meaning the best low possible is A-2-3-4-5 regardless of suits.
• Low hands are counted from the top down, meaning the hand is only as good as its highest card. For example:
  • 2♠ 3♣ 5♥ 6♥ 7♥ is lower than A♠ 2♣ 3♥ 4♣ 8♠
• Any hand with a pair, or with a card higher than 8, does not qualify, even if the rank of the pair is below 8.
• Suits do not count toward a low; any poker lenses players sharing the exact same low must equally split the low half of the pot. (Winning half of the Low pot, and nothing from the High pot is known as being quartered.)

A hand example:

Board: 4♥ 5♣ 7♥ Q♠ A♦
Hand 1: A♥ 2♠ K♥ K♠
Hand 2: A♠ 3♠ Q♥ Q♦
High Winner: Hand 2 wins with three-of-a-kind queens: Q♥ Q♦ Q♠ A♦ 7♥
Low Winner: Hand 1 wins with a 7-5-4-2 Low: 7♥ 5♣ 4♥ 2♠ A♥

Here's a more difficult one for you:

Board: K♥ 3♦ 4♦ 8♠ 2♦
Hand 1: A♥ 2♠ Q♦ K♠
Hand 2: 6♥ 7♥ T♦ J♦
High Winner: Hand 2 wins with a flush, jack-high: 2♦ 3♦ 4♦ T♦ J♦
Low Winner: Hand 2 Wins with a 7-6 Low: 7♥ 6♥ 4♦ 3♦ 2♦
In this pot, Hand 2 scoops with the best high and the best low. Many players will think that Hand 1 will win the low because A-2 is a lot lower than 6-7.
Unfortunately, Hand 1 pairs his 2 on the river, meaning he has to use the 8 as his fifth card to make a qualifying Low hand. Even though the majority of Hand 2's cards are higher, Hand 2 is able to use the three lowest cards on the board, making for a low of only seven-high.

General Rules

• If there is an extra odd chip, unable to be split in half, this chip is always added to the pot awarded to the winning high hand.
• If there is no qualifying low hand, the entire pot is awarded to player with the winning high hand.
• Players can win one or both halves of the pot with the same or different cards from their hand.
• A player does not have to announce what half of the pot she's playiing for at the beginning of the hand. This is only required in other variations of poker, known as "declare" games.