US District Judge Carl Barbier's ruling means that the company could face an extra penalty of as much as $18bn.The stock fell around 6%, or 29p, on the news on Thursday."This may look overdone given a maximum fine estimated at US$18bn (47p) may be reduced by several factors and that the market has already discounted some level of penalty," Liberum said on Friday.BP said it "strongly disagrees" with the decision and will appeal.According to Liberum, "there may be some speculation about BP's business in the US until there is greater clarity", though this could be "some way off".The shares recovered slightly on Friday, up0.9% at 459.05p by 10:47.