thats not how insurance works. insurance doesnt see the bill and go...hmmm..we'll pay 13% of that. Insurance has contracted amounts for each and every procedure, and thats what the insurance pays the provider (in this case, the hospital). The EOB (explanation of benefits) sheet probably lists the amount charged (by the provider), amount allowed (as per the contract), how much the insurance pays, and how much the patient is responsible for. Amount charged by providers is always higher than amount allowed, but wow, I've never seen it that high for an appendectomy