A group of companies that band together to self-insure their workers' compensation obligations on a mutual joint-and-several basis are referred to as "self insured funds". These funds are required by statute in every state to purchase excess workers' compensation insurance for protection from large losses. This ensures that the medical bills and lost wages arising from catastrophic work-related injuries to employees will be paid. Until recently, buyers for this type of insurance enjoyed a market with lots of competition, low minimum premiums, and low per-occurrence retentions.