Investors would have made more money holding shares of Europe's largest companies than by betting on stock of businesses, including Debenhams Plc and OAO Rosneft, that held initial public offerings totaling $51.9 billion ( 40.45b) this year.

Shares of companies that sold stock for the first time in 2006 have gained an average of about 2.4 %, according to data compiled by Bloomberg News. That compares with a 6.9% advance in the Dow Jones Stoxx 600 Index.

Debenhams, the second-largest UK retailer, and Saras, owner of the biggest oil refinery in the Mediterranean region, led companies that took advantage of stock markets that were at a five-year high in May to hold IPOs. Dozens have since been forced to cancel share sales after concern about rising interest rates sent markets lower. Companies planning IPOs in coming months may also struggle to lure buyers.

"Going forward, investors will want to be better rewarded and will be more cautious, " said Jens Peers of KBC Asset Management.

"It will be a tougher market for companies though for investors it could be positive."

The news will add pressure on Aer Lingus to moderate expectations for its offer price, said to have a potential range of between 840m and 1b, but would only be formalised when a prospectus is released next week.

"You would expect IPOs to outperform on average, " said Neil Austin, head of new issues at KPMG Corporate Finance in London.

Companies typically sell shares at a discount to their rivals in IPOs and "the quality of new entrants should be better than the mainstream, " he added.

Sources close to Aer Lingus maintain, however, that while they will be "cognisant" of market sentiment when setting the offer price for shares, there are other priorities at work which dictate that the IPO will go forward in any event.

"This flotation is a strategic priority for the company for access to capital to fund growth, " said a source.

"And it's a strategic priority for the government."

The exception among this year's top five IPOs is Standard Life Plc, the fifth-largest UK insurer, whose shares have outperformed the benchmark index since its debut on July 10 by about 9%.