Denver--Lawyers for a group of Colorado motorists claim consumers have systematically overpaid auto insurance premiums for the past 25 years and should be reimbursed, the Denver Post reported Friday. Insurance representatives say if the proposed class-action lawsuit is successful, it could cost the industry at least $300 million. Some estimates put the liability at $1 billion. The case stems from claims by a group of residents that insurers did not inform them that a household needs to pay only once for uninsured and underinsured motorist (UM/UIM) insurance - no matter how many cars or drivers are in the household. A suit filed last year in Boulder District Court claims 33 insurance companies have been selling uninsured motorist coverage for each vehicle in a household, and that policyholders are due the overcharges, the paper reported. The companies failed to properly inform consumers about uninsured-motorist insurance options, and as a result, many policy owners have unnecessarily paid two or even three uninsured-motorist premiums, according to lawyers for consumers trying to certify the class-action suit. Boulder District Judge D.D. Mallard will hear a request by the insurers to dismiss the suit and will issue a written opinion on the companies' request for a dismissal of the suit.