Sales and excise taxes are very regressive. The burden of such excise taxes typically falls more heavily on the lower-income population who pay a larger percentage of their income than the higher-income population. Income and property taxes, on the other hand, are progressive, rates rising progressively as income or values increase. Poor families pay almost eight times more of their incomes in these taxes than the best-off families, and middle-income families pay more than four times the rate of the wealthy. Wealthy people don’t keep buying more of these goods as their income increases. Moreover, excise taxes are typically based on volume rather than price. For example, in the United States, the federal government imposes an excise tax of US$ 0.184 per US gallon of gasoline regardless of the retail value of the gasoline. Exceptions to this general rule exist in cases where a government taxes either the value of the product or both the quantity and the value.