Okla. Stat. tit. 19 § 901.40
If and when an actual cash surplus accrues in any fund for any prior fiscal year, such surplus shall forthwith be transferred to the same fund for the fiscal year next succeeding the year for which the assessments were originally imposed, and shall be used to pay any warrants and interest thereon which may be outstanding and unpaid for such year. After all warrants and interest on such warrants for such year have been paid or reserved for the surplus, if any, shall forthwith be transferred to the next succeeding year for the same purpose. This procedure shall be followed for each succeeding fiscal year or reserved for, and then any cash surplus remaining shall accrue and be transferred to the current fiscal year, to be used to pay any legal warrant and interest charges of such year. The term "actual cash surplus" as used herein, is hereby defined to mean an excess of actual cash actually on hand over and above all legal obligations. Assessments in process of collection shall not be considered in determining the actual cash surplus for any fund for any fiscal year or years.
Okla. Stat. tit. 19, § 901.40