Several states that produce large amounts of fossil fuels rely heavily on severance tax revenue—taxes based on the volume and/or value of oil, natural gas, coal, and other natural resources. On average, severance taxes accounted for less than 2% of state tax collections in 2014, but in three states—Alaska, North Dakota, and Wyoming—severance taxes provided a much larger share of total state tax revenue in that year. Pennsylvania, on the other hand, is considering a severance tax, and currently derives less than 1% of its revenues from a well head fee.
http://www.eia.gov/todayinenergy/detail.cfm?id=22612