Inspired by Kattboots, here are the very basic Omaha rules.
Omaha is very similar to Texas Hold'em and the basic hold'em hands remain the same, along with the usual betting rounds. The difference is, in Omaha, the hands tend to be a lot better as you have more cards to choose from (9 cards)
Hole Cards. Each player is dealt four cards face down.
The Flop. Three cards are dealt face up on the table.
The Turn. A fourth card is dealt to the table.
The River. Finally, a fifth card is dealt to the table.
The five cards on the table are the community cards and your hand is formed by taking two hole cards and three community cards to create the
best poker hand possible. I should stipulate here that it is definitely only two cards from your hole cards; don't get yourself confused by making a hand just 1 or 3 or even all 4 of your hole cards.
Here is an example of a misleading hand:
Your hole cards:
Community cards:

At first glance, it looks like you have a
full house but in reality, it is just trip 9s with an Ace and a King kicker.
In Omaha, you will have more outs as will all other players. Try and choose hands that have pairs with flush draws, straight flush draws and straight draws.
Omaha Hi/LoIn Omaha Hi-Lo, the high hand winner must share the pot with the player with the best qualifying low hand.
There is always a high hand winner but not always a low. For your hand to qualify for low, it must have five different cards, all no higher than an eight. Any two of your your four hole cards are played for high and any two are played for low. Players must play exactly two out of their hands for each direction. Aces are played both high and low. Straights and flushes do not disqualify a hand for low, so a player ending up with A 2 3 4 5 would have an unbeatable low hand and a 5 high straight to play for the high hand.
The best possible starting hand is AA23 double suited i.e. A2 diamonds and A3 clubs. This hand gives you a great chance to scoop both the high and the low hands.
If you are dealt 4 of a kind as your hole cards - you may as well dump them straight away as they are no use at all.
Remember that you only play to scoop the pot, so after the flop, if your high hand is not a certain winner and will probably have to split with the low, or if you are playing for low and don't have a decent shot at the high hand, usually check/fold and get out early.
Slow play most Omaha hands. It is very difficult to run players off in this game and early raises are risky unless you know you can't lose. Avoid playing middle suited connectors.
Don't over bet A2, A3 and 2 3. Watch out for standard flops, like 8 7 6, they can easily turn into straights that can overtake your high pair or trips. Be wary of suited flops that can make a flush. Keep an eye on the raisers chips as players that are close to all-in often throw their chips at the pot Always watch your opponents and make notes when you can. Pay very close attention to your cards. Omaha Hi Lo hands can get confusing and I suggest using the 4 colour deck where you can - don't get caught out thinking you have a straight flush in spades when in fact all you have is a middle straight.
This is just the very basics of what can be a complex and difficult game to play.
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