• Unfavourable Macondo ruling
• Legal complexities mean exact penalty is unclear
• Case could drag on for years
US district court judge Carl Barbier found BP (BP.) guilty of "gross negligence" and "wilful misconduct" this month under the Clean Water Act for its actions leading up to the Macondo oil spill in the Gulf of Mexico in 2010. The guilty verdict implies a maximum penalty of about $18bn (£11bn), equivalent to roughly 47p a share on top of BP's existing provisions of $3.5bn for this particular penalty.