Michael Phelps has left open the possibility that he could try to match, or even surpass, his record golden haul at the London Olympic Games.

Phelps won an unprecedented eight gold medals at the last Olympics in Beijing in 2008 after winning six in Athens four years earlier but has kept everyone guessing about how many he will tackle in London.

The 26-year-old, who has already confirmed he will retire from swimming after London, was expected to reduce his Olympic programme after admitting he had struggled for motivation.

But when the entry lists for next week's US Olympic trials in Omaha, Nebraska, were released, Phelps was down for seven individual events.

Added to the three relays, which Phelps swam at Athens and Beijing, that would give him a total of 10 events, raising the possibility of a mouthwatering finale from the most successful Olympian of all time.

However, it is unlikely Phelps would swim all the events in London as swimmers often add extra events to the trials just as a back-up in case they fail to qualify in one of their expected events.

As expected, Phelps entered the same five individual events he swam in Athens and Beijing - 200 metres freestyle, 100 butterfly, 200 butterfly, 200 individual medley and 400 medley - although he had previously said he was quitting the 400 medley, his most gruelling event.

He also entered the 100 freestyle, which he needs to contest to qualify for the 4x100 freestyle relay, and 200 backstroke, which he also entered at the last trials but did not swim at the Olympics.

Phelps faces stiff competition both at the Olympics and the U.S. trials from Ryan Lochte, the outstanding swimmer at last year's world championships in Shanghai.

Lochte has entered 11 individual events for the trials, including six where he will line up against Phelps.

In the women's races, the versatile Natalie Coughlin entered five individual events as she tries to make her third Olympic team. Teenager Missy Franklin, the rising star of American swimming, also entered five events as she strives to qualify for her first Olympics.

Dara Torres, attempting to make her sixth Olympic team at the age of 45, was entered in the 50 freestyle dash while former world record holder Janet Evans was entered in the 400 and 800 freestyle after making a comeback at age 40.

- Reuters