(This article was originally published Friday.) By David Benoit Of DOW JONES NEWSWIRES NEW YORK (Dow Jones)--A decision Thursday by the U.S. Supreme Court involving foreign investors and companies in shareholder lawsuits could reduce the liability BP PLC (BP, BP.LN) faces from angry shareholders that have seen the oil company's shares plummet. The court specifically said holders of National Australia Bank Ltd. (NAB.AU), which isn't listed in the U.S., couldn't make use of U.S. law to seek damages for alleged transnational securities fraud. The decision also set a sort of litmus test for the law, saying it could only apply to "transactions in securities listed on domestic exchanges, and domestic transactions in other securities." French media company Vivendi SA (VIV.FR) has already said it believes the decision could ease its litigation concerns. While BP has American Depositary Shares listed in New York, the possible exclusion of the oil company's London Stock Exchange traded stock may reduce the potential award under a class-action suit. The company has 18.8 billion ordinary shares in London and about 3.13 billion ADRs on the New York Stock Exchange. A spokesman for BP declined to comment about any litigation matters. Sarah Cave, a partner at international law firm Hughes Hubbard & Reed, said the court's decision could potentially reduce the size of a class action to one-sixth of the previous size by disallowing the London shares. "That's obviously considerably smaller scope of liability," Cave said. "It's very timely considering the various liabilities that they are facing in the U.S." BP's ADRs and London shares on Friday tumbled to a 14-year low. Since the oil rig exploded in the Gulf of Mexico two months ago, more than $100 billion of its market value has been wiped away. What remains somewhat unclear, however, is whether U.S. citizens who have purchased shares on foreign exchanges can sue. Cave said that could also have an impact if it turns out many Americans own BP shares in London. Robert Schachter, a partner at Zwerling, Schachter & Zwerling, LLP, which is leading an early BP shareholder class-action suit, said it is too early to fully grasp how the court's decision will affect his case. He said because National Australia has no U.S.-listed shares, it may be different for BP suits, and he added that BP's business in the U.S. "is by multiple folds much higher" than National Australia's. "Obviously it's a concern," Schachter said. "The short answer is we are looking at the opinion and looking at the facts and how it relates to BP." -By David Benoit, Dow Jones Newswires; 212-416-2458; david.benoit@dowjones.com; (END) Dow Jones Newswires June 28, 2010 07:36 ET (11:36 GMT)