WBEZ reports that Chicago gas prices have jumped to $4.20 a gallon compared to the national average of $3.69 a gallon. Part of the reason behind the disparity stems from the rise in corn prices due to the Midwest drought.

The Federal Renewable Fuel Standard requires that a minimum level of corn-based ethanol be blended into gasoline, which works to about 13 billion gallons this year. The higher of price of corn this year means that fuel producers must spend more to purchase the federally required ethanol blend.