Global gold prices may have been manipulated on 50 percent of occasions between January 2010 and December 2013, according to analysis by Fideres, a consultancy.

The findings come amid a probe by German and UK regulators into alleged manipulation of the gold price, which is set twice a day by Deutsche Bank, HSBC, Barclays, Bank of Nova Scotia, and Societe Generale in a process known as the London gold fixing.

Fideres' research found the gold price frequently climbs (or falls) once a twice-daily conference call between the five banks begins, peaks (or troughs) almost exactly as the call ends, and then experiences a sharp reversal, a pattern it alleged may be evidence of "collusive behavior."

This "is indicative of panel banks' pushing the gold price upwards on the basis of a strategy that was likely predetermined before the start of the call in order to benefit their existing positions or pending orders," Fideres concluded.

"The behavior of the gold price is very suspicious in 50 percent of cases. This is not something you would expect to see if you take into account normal market factors," said Alberto Thomas, a partner at Fideres.

Alasdair Macleod, head of research at GoldMoney, a dealer in physical gold, added: "When the banks fix the price, the advantage they have is that they know what orders they have in the pocket. There is a possibility that they are gaming the system."

Pension funds, hedge funds, commodity trading advisers, and futures traders are most likely to have suffered losses as a result, according to Mr. Thomas, who said that many of these groups were "definitely ready" to file lawsuits.

Daniel Brockett, a partner at law firm Quinn Emanuel, also said he had spoken to several investors concerned about potential losses.

"It is fair to say that economic work suggests there are certain days when the five banks are not only tipping their clients off but also colluding with one another," he said.

Matt Johnson, head of distribution at ETF Securities, one of the largest providers of exchange-traded products, said that if gold price collusion is proven, "investors in products with an expiry price based around the fixing could have been badly impacted."

Gregory Asciolla, a partner at Labaton Sucharow, a U.S. law firm, added: "There are certainly good reasons for investors to be concerned. They are paying close to attention to this and if the investigations go somewhere, it would not surprise me if there were lawsuits filed around the world."

All five banks declined to comment on the findings, which come amid growing regulatory scrutiny of gold and precious metal benchmarks.

BaFin, the German regulator, has launched an investigation into gold-price manipulation and demanded documents from Deutsche Bank. The bank last month decided to end its role in gold and silver pricing. The U.K.'s Financial Conduct Authority is also examining how the price of gold and other precious metals is set as part of a wider probe into benchmark manipulation following finding of wrongdoing with respect to LIBOR and similar allegations with respect the foreign exchange market.

Fears Over Gold Price Rigging Put Investors on Alert; German and UK Regulators Investigate