South Carolina's two largest revenue sources are Federal Funds derived from the Federal Motor Fuel User Fees and State Motor Fuel Revenues derived from the State Motor User Fees. These two revenue sources account for over 80% of SCDOT total revenues with the Federal Funds contributing the largest share. Federal Funds can only be used on about half of the state-controlled highway system. The section below gives more detail on SCDOT Revenues and Expenditures