Despite a universal insurance mandate, 30 million drivers in the United States do not carry the minimum automobile insurance required by law. Traditional contracts pool high and low frequency drivers and require large upfront payments to enroll. High upfront premiums may make these contracts unappealing to low income drivers, who also drive fewer miles on average. We introduce a flexible "prepaid" auto insurance contract designed to increase take-up among uninsured drivers by lowering liquidity requirements and charging drivers an incremental premium per day of driving. We randomize auto insurance contract offers to uninsured drivers in California (where 15% of drivers lack insurance), varying the flexibility of the contract (traditional versus prepaid), the price of coverage, and quantity discounts for longer coverage terms. The design tests the potential of flexible prepaid contracts to increase insurance take-up among uninsured drivers, estimates willingness-to-pay for lower liquidity requirements, and explores potential barriers to insurance take-up.