Has the undyed diesel tax rate increased? Yes. Beginning July 1, 2017, the undyed diesel tax rate is increased to 21 cents. See important notice 17-08 for rate increases for subsequent years. December 11, 2017 15:43 Related articles Has the undyed diesel tax rate increased? Has the compressed natural gas tax rate increased? What qualifies for a Tennessee agricultural exemption? What are the new refund tax rates for gasoline and diesel? Should petroleum products be billed and reported in gross gallons or net gallons?