As gas prices continue to fall, some Americans believe that the federal government should raise its gas tax, which has been unchanged at 18.3 cents per gallon since 1993. Yet, despite a clear need to bolster transportation and infrastructure funding, which often comes from taxes on gasoline, Congress appears to have little interest in raising the fuel tax.

With the federal government apparently disinterested in raising fuel taxes, some states have taken the lead in funding transportation. According to Michael Green, a spokesman for AAA, “Many states have taken it upon themselves to address the challenges associated with paying for roads, and other transportation projects.”

Click here to see the states with the highest (and lowest) gas taxes

24/7 Wall St. reviewed effective gas tax rates in each state, as summarized by the American Petroleum Institute. We then compared the state’s tax rate against the average gas price in the state. The share of fuel prices that are paid in taxes and fees has risen as gasoline has gotten cheaper. In a few states, taxes make up 15% or more of the price per gallon, including accounting for more than 21% of the gas price in Pennsylvania. Still, taxes in eight states account for less than 10% of the retail price of gas.

Not every state with a low gas tax, relative to the national average price, has a major incentive to increase the amount consumers pay. For instance, Alaska derives much of its tax revenue from oil production, and has historically had less use for a gas tax. However, in some states, the argument for a higher gas tax is likely more compelling. For New Jersey, which has the second lowest fuel tax and is constrained by substantial debts and pension liabilities, a gas tax hike could help it improve its infrastructure.

In some instances, states may not have the ability to raise more revenues from gas taxes, however. New Yorkers already pay more than 45 cents per gallon in fuel taxes, and generally face one of the nation’s highest tax burdens. Thus, even at current low prices, it may be politically difficult for the state to raise fuel taxes.

One major complicating factor is that some states peg their fuel tax to the price of gas. As gas prices drop, the amount these states can collect will also fall, especially if the drop in prices substantially outweighs the extra amount Americans are willing to drive.

Another complicating factor in deciding how to tax gas is that the market for gasoline differs substantially across the U.S. States in the Southeast, for example, are home to some of the nation’s least expensive gas, Green explained, “because these are states that are near major refineries, and also those refineries have access to domestic crude oil.” California, on the other hand, typically has higher gas prices because its refineries consistently run at or near capacity to meet demand for the state’s specific, legally-required blend of gasoline.

In order to identify the effective gas tax in each state, 24/7 Wall St. reviewed January 2015 data from the American Petroleum Institute. We also reviewed data on gas prices from AAA’s Daily Fuel Gauge Report for January 14, 2015. Figures on state infrastructure are from either the Federal Highway Administration, or the American Society of Civil Engineers’ Infrastructure Report Card. Figures on per capita taxes are from the Tax Foundation, while information on states’ oil production, consumption and infrastructure comes from the Energy Information Administration (EIA).

These are the states with the highest (and lowest) gas taxes: