S.C. Code Ann. § 12-6-2320
(A) If the allocation and apportionment provisions of this chapter do not fairly represent the extent of the taxpayer's business activity in this State, the taxpayer may petition for, or the department may require, in respect to all or any part of the taxpayer's business activity, if reasonable:
(B)
(1) For the purposes of this chapter, the department may enter into an agreement with the taxpayer establishing the allocation and apportionment of the taxpayer's income for a period not to exceed five years, if the following conditions are met:
(3) Notwithstanding the provisions of item (1), the department may enter into an agreement with the taxpayer establishing the allocation and apportionment of the taxpayer's income for a period not to exceed ten years if the following conditions are met:
(a)