Rules which required assets to be valued at market prices - called fair-value or mark-to-market - were eased in October to allow European companies to use higher prices for derivatives when they reported earnings from the third quarter of 2008.

Dropping mark-to-market accounting could have helped many financial groups avoid reporting an immediate loss, but most of them declined to do so. The EU market supervisors did not give a reason why.

U.S. regulators have resisted a banking industry push to suspend mark-to-market rules, saying accounting standards shouldn't be bent to help the troubled economy.

But CESR, the committee of European securities regulators, said that more than half of 100 banks and financial groups it looked at and almost two-thirds of companies listed on the FTSE Eurotop 100 index did not reclassify any assets in the third quarter.

Only a fifth of banks and 18 percent of major financial groups shifted investments from one category to another, most opting to reclassify fair-value investments through profit and loss - which are depressed at current market prices - as loans and receivables.

No company chose to reclassify assets in the longer-term by relabeling them as held-for-maturity, which would have allowed them to increase the value of those assets on their balance sheets.

CESR warned that its figures were based on interim financial statements and it would watch out for any updates companies may publish this spring.

The financial crisis saw EU regulators soften the accounting rules under pressure from some businesses that claimed they needed the same flexibility as U.S. companies to avoid recording ballooning losses on their balance sheets as market prices for derivatives slid.

Traders have lost confidence in these repackaged investments in recent months, fearing they may be based on so-called "toxic assets" such as mortgages made to people with poor credit that are unlikely to be paid back promptly during an economic downturn.