ICC World Twenty20 winner is anyone's guess

The World Twenty20 explodes into action this week in tropical Sri Lanka with no runaway favourite and upsets likely in cricket's shortest and least predictable form.

At least half of the 12 participating nations will consider themselves strong contenders to lift the trophy in Colombo on October 7, with the others hopeful of living up to the event's reputation for shocks.

From defending champions England, the powerful West Indies and formidable South Africa to Asia's top three -- former winners India and Pakistan, and Sri Lanka -- the field is strong and deep.

The others won't be taken lightly either, if a string of sensational results in the tournament's three previous editions are any indication.

While many purists are unconvinced by Twenty20, and fear the impact on Test cricket, there's no doubting its entertainment value.

India, initially reluctant to embrace the newest format, won the inaugural event in South Africa in 2007 under rookie skipper Mahendra Singh Dhoni after senior pros Sachin Tendulkar, Rahul Dravid and Sourav Ganguly opted out.

It was in the same tournament that Zimbabwe stunned Australia, Bangladesh upset the West Indies, and India brushed aside England, South Africa, Australia and Pakistan in successive games to grab the title.

Pakistan won the second edition in England in 2009, a tournament that made a stunning start when the Netherlands, a non Test-playing nation, upset the hosts by four wickets in front of a packed house at Lord's.

England claimed the 2010 title in the Caribbean, but it was Australia's amazing win over Pakistan in the semi-final that remained the talking point.

With 34 needed from the final two overs, Michael Hussey smashed 38 off 10 balls to take Australia home with one delivery to spare.

Only last week, Australia trounced Pakistan by 94 runs to avenge two successive defeats against the same opponents.

"It's the sort of format where nothing can be taken for granted," said India's Dhoni. "We have seen one ball change the whole game. "The idea is to do well for all the 40 overs. That is all that matters."

The 12 sides have been divided into four pools for the preliminary league, with the top two from each advancing to the Super Eights round.

If the seedings go to plan, fans can expect high-voltage action in the Super Eights -- a week-long race to the one-off semis and final in the Sri Lankan capital.

England, the West Indies, Sri Lanka and New Zealand are seeded to meet in group one of the Super Eights, with the top two teams making it to the semi-finals.

Group two is already being billed as the "Group of Death", with arch-rivals India and Pakistan seeded to face Australia and South Africa.

Sri Lanka's frontline batsman Kumar Sangakkara cautioned rivals not to expect spin-friendly pitches at the three venues in Colombo, steamy hill town Pallekele and Hambantota, site of a major new port.

"Be ready for a stiff breeze in Hambantota, swing and seam in Pallekele and a good batting surface at the Premadasa (stadium) in Colombo," the veteran batsman-wicketkeeper said.

"Each venue will have a different challenge and sides will have to adjust accordingly. It will make the tournament more exciting."

England are out to prove they can defend the title without star batsman Kevin Pietersen, the man of the tournament in 2010 who has been axed from the national team on disciplinary grounds.

The West Indies are touted as potential champions, with explosive batsmen in Chris Gayle, Kieron Pollard and Marlon Samuels, and a wily spinner in Sunil Narine.

The men to watch out for are plenty. Australian spinner Brad Hogg, aged 41, and South African all-rounder Jacques Kallis, 37 next month, will look to rubbish the theory that Twenty20 is a young man's game.

Ace Indian all-rounder Yuvraj Singh is assured of a warm welcome from the stands, having battled cancer earlier this year to return to the big stage.

Also vying for the spotlight will be prolific Pakistani spinner Saeed Ajmal, dashing Australian opener David Warner, local boy Lasith Malinga, England's Jonny Bairstow and South African Richard Levi.