Omaha 8 is a community card poker game similar to Texas Hold’em, where each player is dealt four cards and must make his best hand using exactly two of them, plus exactly three of the five community cards.
Omaha 8 is also a ‘ hi-low split’ game. That is to say, at the end of the hand, the pot is divided into two. The best high hand takes half the pot, and the best low hand takes the other half.
The high hand is calculated in the same way as in normal (high only) Omaha. You must take any two cards from your hole cards, and any three cards from the board, to make the best five card hand you can. Note the difference to Texas Hold’em, where you may use two, one or even zero of your hole cards. In Omaha and Omaha 8, you must use precisely two of your hole cards.
To make a low hand, you again take two of your hole cards and three cards from the board. Your aim is to make a five-card hand with five cards ranked eight or below. Note that the five cards making up the low must each be of a unique rank (e.g. a starting hand of A-A-9-9 can never make a low because you only have one unique card of 8 or lower).
It will not always be possible to make a low. For example, if you hold A-2-3-4 in your hand, the board still has to show three unique cards of eight or below for your low to qualify. If the board only shows two cards below eight (e.g. 6-7-J-J-K) it does not matter that you have three low cards in your hand. No low is possible.
The best possible low hand in Omaha 8 is the wheel, A-2-3-4-5. It does not matter for the low that a wheel is also a straight. Equally it does not matter for the low if the five cards are all of the same suit. A wheel is a strong hand as you have a straight for a high and the best possible low.
Also published here 888.com eMagazine Poker Strategy: Omaha starting hands.