The 11th U.S. Circuit Court of Appeals has upheld a lower court's finding that a U.S. treasure-hunting firm must hand over to Spain $500 million in gold and silver coins salvaged from the bottom of the Atlantic in May 2007.

"Now the only thing left for them is to go to the U.S. Supreme Court, though if they're realists they should see they're defeated," the attorney representing Spain in the legal battle with Odyssey Marine Exploration, Inc., James Goold, told Efe Wednesday.

The latest decision confirms one issued in September by a three-judge panel of the appellate court in Atlanta.

Odyssey, based in Tampa, Florida, expected the 11th Circuit to reject the appeal, according to the firm's vice president and general counsel, Melinda MacConnel.

"We plan to appeal to the U.S. Supreme Court and we have 90 days to do so," she told Efe.

Goold pointed out that the Supreme Court "receives an average of 5,000 requests a year for review of cases and of those it hears only around 80."

Moreover, he said, the high court refused in February 2001 to review an appellate court decision establishing Spain's right to the remains of two colonial-era Spanish frigates that sank off the coast of Virginia.

"There is a clear message here. With that jurisprudence, I see no reason why the Supreme (court) could accept a review of the decision in this case," Goold said.

U.S. District Judge Steven D. Merryday ruled in December 2009 that Spain was the rightful owner of the treasure Odyssey salvaged off the Portuguese coast in the same area where the Nuestra Señora de las Mercedes, a Spanish navy frigate, was destroyed in battle in 1804.

Within days of recovering the $500 million in coins, Odyssey took the hoard to Gibraltar and loaded it onto a chartered Boeing-757 for transport back to Florida.

The treasure remains at a secret location in Florida.

Madrid says the treasure came from the Mercedes and that the vessel and its contents rightfully belong to Spain under the principle of sovereign immunity.

Odyssey, however, contends that contemporaneous Spanish diplomatic communications show the Mercedes was on a commercial mission at the time of her sinking, invalidating Madrid's sovereign immunity claim.