This paper examines, theoretically and through a series of simulations, the effect of a pay-at-the-pump auto insurance system where the minimum amount of insurance required by California law is paid through a fuel surcharge. Vehicle fixed costs are reduced while variable costs increase. The results show that gasoline demand would be reduced by roughly two to five percent in 1998 (with greater percentage drops in later years), while VMT would drop by slightly less as the incentive to drive more fuel efficient vehicles reduces exposure to the tax. At the same time, pay-at-the-pump is shown to improve the welfare of the average California driver as insurance is priced more efficiently. In other words, unlike other transportation pricing measures that have been proposed in the recent past (VMT and fuel taxes, pollution fees, etc.), PATP may offer a means of reducing the external costs of transportation (global warming, congestion, etc.) without raising private costs for the average motorist. Another appealing aspect of PATP may be its apparently progressive nature-the lowest income households may see the highest gains in welfare.