Omaha is a game predominantly played around the nuts
Due to the fact that you have to use exactly two of the cards from your hand in Omaha, holding just the ace (or king for that matter) of a suit will never enable you to have the nut flush. It does, on the other hand, bring up good opportunities to bluff if the moment is right.
As Omaha is a game predominantly played around the nuts, knowing that your opponent cannot have the nuts (due to you holding the crucial card) can allow you to really exert pressure on any tight Omaha player if the nut flush (which you know cannot be held by anybody), is the best hand on a particular board.
These sort of plays in Omaha not only enable you to pick up some nice pots against tight players, but they can also make you a fortune if you get caught doing it by a stubborn player who cant fold their smaller flush. If players see you making these sorts of bluffs in Omaha, they will often start calling you down extremely light in the future. Omaha is an extremely easy game to make money from if players just start calling you down, as all you have to do is just sit back and continually bet your big hands - being able to get a lot of action makes your life very easy in Omaha.
As with any bluff, the story you tell has to be consistent with you having the hand when you make this play, and depending on whether you are in or out of position various tricks can be employed. One of my favorites when playing out of position is setting up a river check raise against a tight player. Say the flop contains two clubs and you hold the ace of clubs and bet the flop. The tight player calls and you see a club turn. You bet again and the tight player calls. Here that players range is limited really to a set or a lower flush. Assuming the river does not pair, a great play here is to check raise the river if they bet out. To a tight, thinking player, it is basically impossible for them to call here - in their mind you simply cannot really be bluffing.
Other good plays like this include check raising the turn and betting the river, or simply firing three barrels and seeing if your opponent can stand the pressure. Omaha throws up some great opportunities for making creative bluffs, bluffing the ace flush is one of the most satisfying,and even if it goes wrong, it will nearly always give you great future action when you actually have it.
Play Omaha Poker at Betfair Poker