Federal law. In resolving contribution claims, the court may allocate response costs among liable parties using such equitable factors as the court determines are appropriate. Nothing in this subsection shall diminish the right of any person to bring an action for contribution in the absence of a civil action under subsection (a), (k), or (l) of section 7. (f) Period in Which Actions May Be Brought (1) Response period An action under section 7(a) or (k) of this title must be commenced within three years of the commencement of the response action or within three years of the date on which the Government bringing the action knew or ought reasonably to have known the identity of the nongovernmental operator, whichever is later. In no event shall an action against a nongovernmental operator be commenced later than 15 years after the commencement of the response action. (2) Cost recovery period An action under section 7(e) of this title for contribution toward costs incurred pursuant to section 7(a) or (b) must be commenced within three years of the date of judgment in any action under section 7(a) or (k) for recovery of such response costs or in the absence of such an action, within three years of the date that the person seeking contribution knew or ought reasonably to have known the identity of the nongovernmental operator. (3) Cost contribution period An action under section 7(e) for contribution toward response costs assessed pursuant to section 7(l) must be commenced within three years of the date of the assessment or within three years of the date of any judgment under subsection 7(l)(vii), whichever is later. (g) Liability cost limit The maximum amount for which each nongovernmental operator may be liable for the costs of response actions under sections 7(a), 7(k), or 7(l), in respect of each environmental emergency, shall be as follows: (1) For an environmental emergency arising from an event involving a ship: (A) one million SDR for a ship with a tonnage not exceeding 2,000 tons