"Equitable contribution is . . . the right to recover . . . from a co-obligor who shares such liability with the party seeking contribution. In the insurance context, the right to contribution arises when several insurers are obligated to indemnify or defend the same loss or claim, and one insurer has paid more than its share of the loss or defended the action without any participation by the others. . . . Equitable contribution permits reimbursement to the insurer that paid on the loss for the excess it paid over its proportionate share of the obligation, on the theory that the debt it paid was equally and concurrently owed by the other insurers . . . . the purpose of this rule of equity is to accomplish substantial justice by equalizing the common burden shared by coinsurers, and to prevent one insurer from profiting at the expense of others. "The reciprocal contribution rights of coinsurers who insure the same risk are based on the equitable principle that the burden of indemnifying or defending the insured with whom each has independently contracted should be borne by all the insurance carriers together, with the loss equitably distributed among those who share liability for it . . . ." (Fireman's Fund Ins. Co. v. Maryland Casualty Co. (1998) 65 Cal. App. 4th 1279, 1293-1294 [77 Cal. Rptr. 2d 296], italics and fn. omitted.) The right to contribution " 'do[es] not arise out of contract, for [the coinsurers'] agreements are not with each other . . . . Their respective obligations flow from equitable principles designed to accomplish ultimate justice in the bearing of a specific burden. As these principles do not stem from agreement between the insurers, their application is not controlled by the language of their contracts with the respective policy holders.' " (Signal Companies, Inc. v. Harbor Ins Co. (1980) 27 Cal. 3d 359, 369 [165 Cal. Rptr. 799, 612 P.2d 889, 19 A.L.R.4th 75] (Signal Companies).) Even so, absent compelling equitable reasons, courts should not impose an obligation on an insurer that contravenes a provision in its insurance policy. (Signal Companies, supra, 27 Cal. 3d at p. 369.) Further, our Supreme Court has "expressly decline[d] to formulate a definitive rule applicable in every case in light of varying equitable considerations which may arise, and which affect the insured and the primary and excess carriers . . . ." (Ibid.) In determining whether one insurer is entitled to contribution from another, " 'courts should consider the nature of the claim, the relation of the insured to the insurers, the particulars of each policy and any other equitable considerations.' " (Fire Ins. Exchange v. American States Ins. Co. (1995) 39 Cal. App. 4th 653, 664 [46 Cal. Rptr. 2d 135]; accord, Signal Companies, supra, 27 Cal. 3d at p. 369.)