BP's shares were down by 0.5 percent in early session trading, adding to a 5.9 percent slump on Thursday.

BP said it would appeal Thursday’s ruling by U.S. District Judge Carl Barbier in New Orleans, Louisiana.

However, some analysts said the court ruling would add an element of uncertainty over the company's financial prospects, due to the risk of more fines and legal costs.

"Judge Barbier's ruling that BP was grossly negligent with respect to the Deepwater Horizon accident and that its activities at the Macondo well amounted to wilful misconduct does come as a surprise and is close to the worst case scenario we could envisage for the stock," Barclays analysts wrote in a research note.

(Reporting by Sudip Kar-Gupta; Editing by Kate Holton)