Sadly, it's due to having the highest tax per gallon of gasoline in the Southern United States. This data is put out by ExxonMobil, which is apparently trying very hard to make us hate big oil even less.
The standard article:
http://www.exxonmobilperspectives.com/2014/02/07/this-gasoline-tax-map-explains-a-lot/
Oh look, they've got an interactive link as well:
http://www.api.org/oil-and-natural-gas-overview/industry-economics/fuel-taxes/gasoline-tax
They've even got a pdf with info from each state:
http://www.api.org/state-taxes/northcarolina.pdf
The standard article:
http://www.exxonmobilperspectives.com/2014/02/07/this-gasoline-tax-map-explains-a-lot/
Oh look, they've got an interactive link as well:
http://www.api.org/oil-and-natural-gas-overview/industry-economics/fuel-taxes/gasoline-tax
They've even got a pdf with info from each state:
http://www.api.org/state-taxes/northcarolina.pdf