I. Except as provided in paragraph II, a right of contribution exists between or among 2 or more persons who are jointly and severally liable upon the same indivisible claim, or otherwise liable for the same injury, death or harm, whether or not judgment has been recovered against all or any of them. Except as provided in RSA 507:7-g, I and IV, the right of contribution may be enforced only by a separate action brought for that purpose. The basis for contribution is each person's share of the obligation, including the proportionate share of the claimant at fault as determined in accordance with the provisions of RSA 507:7-e. No right of contribution exists against a person who is immune to the claim which would otherwise give rise to a right of contribution. No right of contribution exists against the claimant at fault.
II. Contribution is not available to a person who enters into a settlement with a claimant unless the settlement extinguishes the liability of the person from whom contribution is sought, and then only to the extent that the amount paid in settlement was reasonable.