The case was complicated by the fact that policies covering the site were in varying degrees of finality at the time of the attacks.

The Appeals Court ruling did not have any problem with the fact that differing interpretations could be given to differing policies.

“This all-or-nothing supposition is mistaken because it assumes that the congruent coverage was achieved during the binder period, and ignores overwhelming evidence that different insurers issued interim binders governed by different forms,” the ruling stated. “These forms were designed with different interests in mind and, not surprisingly, yielded different results.”

The court went on to stress that the differing rulings were therefore not a manifestation of judicial error, “but rather a reflection of the fact that the parties were at various stages of negotiating coverage when the two hijacked airplanes destroyed the WTC.”

As a result of yesterday's ruling, Swiss Re, Lexington Insurance Company and Lloyd's of London will be able to treat the attacks as one event.

Jacques Dubois, chief executive of Swiss Re America Holding Co., said “today's decision resolves [Mr.] Silverstein's two-occurrence claim once and for all in Swiss Re's favor.”

But Allianz, Zurich American Insurance Company and Travelers Indemnity Co. could have to pay an additional $1.1 billion since they were on the receiving end of the jury verdict that said the attack was two events.

Mr. Silverstein issued a statement saying merely, “The court has spoken and the time has come for all insurers to pay what they owe.”

St. Paul Travelers, parent of Travelers Indemnity and Gulf Insurance Co., issued a statement saying the ruling would have no impact on earnings since it had already been factored into the conglomerate's financials.

The single-multiple event dispute was not the only obstacle to full payment as the transfer of a portion of the site from Mr. Silverstein back to the Port Authority of New York and New Jersey also has raised coverage issues.

Earlier this week, St. Paul Travelers said that it had agreed to honor Mr. Silverstein's claims for the rebuilding of the site after reviewing the implications of the transfer of ownership from developer Larry Silverstein to the Port Authority of that portion of the complex ready for building. But not all the details of the payment have been worked out, the company said.