HOLLYWOOD – Success may come in threes … but there also can be too much of a good thing.

So which will it be in the summer stampede of 2007, when three highly anticipated sequels – each one the third in its respective franchise – debut in the span of just three May weeks?

The head-to-head-to-head clash of “Pirates of the Caribbean: At World’s End,” “Shrek the Third” and “Spider-Man 3” is unprecedented in box office history and could reshape admissions records for the summer. One film in each series claims a spot among the Top 10 highest-grossing movies of all time, and last year’s “Pirates” sequel enjoyed the biggest opening weekend ever.

And now they’re all coming back one atop the other. Spidey starts off the summer May 4, followed on May 18 by the lovable ogre and May 25 bringing back a swashbuckling Johnny Depp.

But do the three-quels offer too much firepower for one month?

“It’s a little bit like the 100-year flood – extremely unusual,” said Paul Dergarabedian of the box-office tracking company Media by Numbers. “But I think the marketplace will expand and we could have the biggest May of all time.” He says “Shrek” should benefit from having a greater share of family moviegoers, while “Spider-Man” and “Pirates” will battle for teens.

However the audiences split, there’s plenty at stake. The three studios behind the three-quels have devoted well more than half a billion dollars in combined budgets to make the movies.

One thing is for certain: Unless one of the movies is completely slaughtered, expect fourth installments from all the participants in the near future. Here is a closer look at each of this summer’s heavyweight contenders.

“Pirates of the Carribean: At World’s End”

Director Gore Verbinski has lost track. “I don’t know how long it’s been,” he said of when he started working on the back-to-back “Pirates of the Caribbean” sequels. After a few minutes’ reflection, Verbinski concludes it’s been 21/2 years. And on this winter day, he’s only just started editing the third film.

If the director’s memory is a bit blurry, it’s not surprising. With each new “Pirates” movie, the filmmaker’s ambitions evolve. At first, Verbinski says, he was simply trying to blend swashbuckling with Monty Python. “We thought they’d never let us make a pirate movie,” he said.

But that first movie was a 2003 blockbuster, and Disney seemed to like what Verbinski and writers Ted Elliott and Terry Rossio were up to. “The second time we thought, ‘We’re not making them nervous.’ And that was scary,” Verbinski said. “You’re trying to mess with the system, and the system says, ‘Right on, brother!’”

So Verbinski promises that the next – but probably not last – installment in his franchise will revert to more storytelling mischief. “We thought maybe we have to scare ourselves in terms of the absurdity and level of funk. We want to destroy the genre that we resurrected. We defined it. And now we want to kill it.”

When we saw Jack Sparrow (Depp) last summer in “Dead Man’s Chest,” he was paying the price for selling his soul to the devil (in the form of Davy Jones), and the fey buccaneer was left stuck inside a giant sea monster when the credits rolled. For the third film, the challenge is to get Sparrow out.

The cast of characters continues to expand. For the third movie, Chow Yun Fat joins as Sao Feng, the pirate lord of Singapore, who is battling the ruthless East Indian Trading Co., headed by Lord Cutler Beckett (Tom Hollander). Where computer-generated sea and pirate creatures shared screen time in last summer’s film, water itself will have a costarring role in the new sequel.

And if double-crossing was part of every other characters’ personality in the second film, it’s only natural that triple-crossing would be a mainstay in the third.

“Shrek the Third”

He’s still an ogre. But Shrek has never looked better.

“It’s astounding, the leaps we keep making (in technology),” said Aron Warner, who has produced all three “Shrek” films, including the upcoming sequel. “The facial features are improved each and every time. There’s increased details in the use of the muscle system. The texture and lighting feel more tactile, but not in a way that takes you out of the movie.”

And much of that, Warner says, is what gives “Shrek the Third” an advantage in competing against “Pirates” and “Spider-Man.”

“If you’re going to have three (high-profile) movies come out, you might as well pick three different films,” he said. “That’s the good thing about it. We’re the only pure comedy of the three.”

Warner notes “Shrek 2” faced similarly high-profile opposition (it debuted in the midst of “Van Helsing,” “Troy” and “The Day After Tomorrow”) and wasn’t hurt.

Audiences clearly have embraced the adorably ugly green beast in his previous incarnations and DreamWorks is confident there’s no “Shrek fatigue” settling in just yet.

When we last met the odorous ogre, his marriage to Fiona left him in line to become king. But when his father-in-law falls ill, Shrek (voiced by Mike Myers) has second thoughts about ascending the throne. With his trusted companions Donkey (Eddie Murphy) and Puss in Boots (Antonio Banderas), Shrek searches for a suitable replacement, finding a promising candidate in Fiona’s 16-year-old cousin Artie, an underachieving medieval high school slacker (Justin Timberlake).

“Spider-Man3”

Director Sam Raimi recalls sitting among a batch of theater owners in Las Vegas several years ago waiting to screen his then-latest film, “Spider-Man 2.” Before it even started, Sony chief Amy Pascal announced to his surprise that the studio was making “Spider-Man 3” and releasing it on May 4, 2007.

“I looked around and said, ‘We don’t have a story!’” Raimi recalled. “She decided it will happen, and she’s very powerful. Suddenly, we had a release date and everything gets built backward from there.”

For Round 3, the filmmaking team decided to strike for new territory: Spider-Man (Tobey Maguire) is apparently going to get his Darth Vader moment. “It’s a journey to Peter Parker’s dark side,” explained Raimi, who with his brother Ivan, screenwriter Alvin Sargent, and producers Laura Ziskin and Avi Arad came up with a tale of hubris Spidey style.

“It’s a metaphor for how somebody who’s on top can stumble and lose sight of those things which are important and fall into a darkness, a blackness of the heart,” said Raimi, who directed the first two installments. “Then, because it’s a story of Spider-Man, this heroic figure, he finally finds his way out, of course. … This is a story about a character who falls into his pride.”

Along the way, Spider-Man gains two new enemies: Sandman (Thomas Haden Church), who’s a shape-shifter and can manipulate sand, and Venom (Topher Grace). Venom is essentially the same creature as Spider-Man, but “more powerful and faster. He’s supposed to represent the anti-Spider-Man,” Raimi said.