Pot Limit Omaha is another one of the most action packed and popular games available at the moment. It's a great balance of skill and luck; with the number of hand combinations that are possible making for constant action and big pots.
Pot Limit Omaha is structured exactly the same as Texas Hold'em--but players are dealt four cards instead of two. Unlike Hold'em, where you can use one--or even none--of your hole cards to make the best hand, Pot Limit Omaha requires you to use two cards of your hand at showdown. As an example, holding the ace of clubs in your hand when there are four clubs on the board gives you a flush in Hold'em, regardless of what your other card is. In contrast, Pot Limit Omaha requires that you must have two clubs in your hand in order to have a flush in this situation.
Just like in Texas Hold'em, Pot Limit Omaha uses a system of forced bets called 'blinds'. These are two bets made before the cards are dealt, one small and one big, that slowly rotate around the table with the dealer button to ensure everyone pays them equally. They always fall to the left of the dealer button, with the small blind on the immediate left of the dealer, and the big blind to the immediate left of the small blind.
Although it can be played as both a limit or a no limit game, Omaha is nearly always played as a pot limit game because neither of the other formats quite suit the game. This means that you can bet up to and including the size of the pot at any point, but no more.
Omaha is also played as a High/Low split game, with a full guide to this form of Omaha available here.
Pot Limit Omaha is one of the most interesting, complex, and action packed games available. The possibilities for each hand are nearly infinite; and it produces situations unlike any other poker game. It has been steadily growing in popularity over the last few years, and is now a staple of the highest stake games in the world with millions of dollars being won and lost in the biggest Pot Limit Omaha games.