Omaha High is very popular in European card rooms as well as the major rooms online. U.S. card rooms don't seem to spread the game often. When they do, it tends to be a "big game" played pot-limit with large blinds.
Omaha is usually played using the pot-limit betting structure in live games but you can also find no-limit and limit games online. Limit Omaha is particularly unpopular.
On its face, Omaha looks quite a bit like Texas hold'em. The betting is similar and there's a flop, turn and river. The obvious difference is that each player is dealt four cards rather than two. The only major mechanical difference is on the showdown. The game is played only for high but you must use two cards in your hand and three cards on the board.
Otherwise the rules are the same as for standard Texas hold'em of the same betting structure.
Omaha high is commonly referred to as a game of the nuts. If you don't have the nuts or a strong draw to the nuts, it's probably best to avoid heavy action.
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