Omaha Hi/Lo is a variant of Omaha. The betting, blinds, and postings are exactly the same as in Omaha. If you're not familiar with Omaha, click here for a quick lesson. At the showdown, the pot is split between the holder of the highest hand, and the holder of the lowest hand, if the low hand qualifies.
To qualify for a low hand, you must have five distinct cards (no pairs), with no card higher than an 8. Remember, since you have to play two cards in your hand, the two cards in your hand and three on the board all need to be 8 or lower. Straights and flushes do not count against you. The best 5-card low hand is A-2-3-4-5 of any suit. The hand is "ranked" by starting with the highest low card. 7-4-3-2-1 would be considered a 7-low, and would lose to 6-4-3-2-1, a 6-low. If two players each have low hands with the same highest card, the next highest card determines the winner. 7-5-4-3-2 loses to 7-4-3-2-1. If there is no qualifying low hand, the high hand wins the entire pot.
Just as in the high version of Omaha, each player starts with four hole cards, and then the dealer places five cards face-up in the center of the table. These community cards are part of each player's hand, so each player has access to seven cards. The difference between Omaha high and Omaha Hi/Lo, is that in Omaha Hi/Lo each player can potentially have two different hands: a high hand and a low hand.
Each player forms a five-card high hand by using only two (no more, no less, but they can be any two) of his hole cards together with only three (no more, no less, but they can be any three) of the five community cards. Each player forms a five-card low hand (if possible) by using only two (no more, no less, but they can be any two) of his hole cards together with only three (no more, no less, but they can be any three) of the five community cards. Both the high hand combination and the low hand combination can use the same set of cards, but they don't have to; in fact, usually they would not.
Because of the qualifier restriction, if at least three cards 8 or lower do not appear among the community cards, a low hand is not possible.
For more information on how to play Pot Limit Omaha, go to: Omaha Hi/Lo Comprehensive.