S.C. Code Ann. § 12-6-2810

Payment of tax otherwise due under this chapter on income attributable to the increase in gross income from foreign trading receipts may be deferred until the taxpayer intentionally ceases exporting property, or until after three taxable years in which the taxpayer has no gross income from foreign trading receipts, whichever is earlier, provided the base amount defined in Section 12-6-2850(3) does not exceed five million dollars, and the taxpayer pays interest annually on the aggregate deferred tax at the base period T-bill rate. The interest is due on the date the taxpayer is required to file the annual return required by this chapter without regard to any extension.