R.I. Gen. Laws § 44-11-2.1: Surtax.

Each corporation whose taxable year ends on or after March 31, 1991 and before January 1, 1994 shall annually pay to the state a surtax of 11% on the amount of the tax computed under § 44-11-2. The surtax shall be added to the amount of the tax computed under § 44-11-2 in computing the total tax due by the corporation for the taxable year or years under this chapter. The estimated tax provisions of chapter 26 of this title shall apply to the surtax.