In throwing out the case's class-action status, the appeals panel also erased the plaintiffs' ability to allege that defendants Merrill Lynch & Co., Credit Suisse First Boston and Barclay's were primary participants in fraud that helped fuel Enron's failure in December 2001.

When U.S. District Judge Melinda Harmon granted class-action status last year, her ruling included that the plaintiffs could argue that the banks were primary participants rather than bit players. If a jury agreed, they could be held liable for their own actions as well as everyone else deemed to be involved.

Such a finding could have led to a multibillion-dollar judgment in excess of the $7.3 billion in settlements already reached — the bulk of which came from banking titans J.P. Morgan Chase, Citigroup and the Canadian Imperial Bank of Commerce.

The appeals panel ruled that Harmon erred in giving plaintiffs that much latitude, saying the deals the banks conducted with Enron "at most aided and abetted Enron's deceit."

The Securities and Exchange Commission can pursue aiders and abettors, but civil securities litigation can only pursue primary violators.

The plaintiffs countered in today's filing that the banks were at the epicenter of fraud, cooking up financial structures and schemes to help Enron doctor its financial statements.

Spokesmen for all three banks, which have consistently denied the plaintiffs' allegations, declined comment today.