The risk of bankruptcies among the big US homebuilders has risen sharply as the economy has weakened and an end to the housing slump remains distant.

Credit default swaps on homebuilders, which act as insurance on corporate debt, suggest some of the biggest are at risk of failing to keep up debt payments. According to Byron Douglass, an analyst at Credit Derivatives Research, the most exposed are Standard Pacific, Hovnanian (NYSE: HOV - News) , Beazer, and Meritage. All are among the top 15 publicly-listed US homebuilders.

Mr Douglass said bankruptcies were "highly likely" among top homebuilders. Homebuilding is viewed as being the sector most threatened by the slowdown as housing has been the worst hit part of the economy.

Tousa, formerly Technical Olympic, became the largest homebuilder so far to file for bankruptcy. At least 13 other homebuilders have gone bankrupt since June, according to Bloomberg data.

Sales of newly built homes last year suffered the biggest fall since records began in 1963. The top US homebuilders have written off nearly $20bn since 2006 because of falling house and land prices.

"They are at the epicenter of what. . . is going to be a pretty bad recession," Mr Douglass said. "The first companies we are going to see defaults on are homebuilders."

Defaulting on debt is "in most cases coincident with bankruptcy," said Robert Curran, an analyst at Fitch Ratings.

"This action is necessary to reflect the realities of today's homebuilding market," Antonio Mon, Tousa's chief executive, said in a statement.

Homebuilders have been frantically trying to sell off their homes and raise cash to remain liquid, offering heavy discounts and making large losses.

Spreads on five-year credit default swaps suggest the most at risk builder is Standard Pacific, which on Tuesday had a 79 per cent probability of default, according to calculations by Mr Douglass. Shares in the company are down 93 per cent this year.

The spread of 32 per cent up front on Standard Pacific CDS means that to insure $10m of Standard Pacific debt for one year costs $3.7m. The market for CDS is not a precise indicator and, because it is risk averse, can tend to exaggerate the threat of default.

Standard Pacific declined to comment.

Standard Pacific is seen at particularly at risk of default because it has the second largest amount of joint ventures in the homebuilding industry.

"It has a lot of hidden negative issues related to partnerships," said Mr Curran.

According to Mr Douglass's calculations, Hovnanian has a 70 per cent risk of default, and Beazer has a 68 per cent risk. A spokesperson for Beazer said the company had "$325 million in cash and no borrowings on our revolving credit facility and no long term maturities before 2011". Hovnanian did not return calls.

Meritage has a 66 per cent risk of default. A Meritage spokesman said it was "in compliance with all our covenance right now".

The biggest homebuilders, including Lennar, KB Home and DR Horton, are all thought to be widely-enough spread in the US and to have shored up their balance sheets to avoid collapsing.

"Builders are doing what they need to do to survive this downturn," said Nishu Sood, an analyst at Deutsche Bank. "But homebuilding is a ship which turns very slowly, so some may not survive."