Okla. Stat. tit. 70, § 135c

Reimbursement to the county for the expense to such county for the salary and bond of such deputy of school accounts shall be accomplished in the following manner: The amount of the annual salary of such deputy shall be ratably charged to each school district, dependent and independent, so served, in ratio of the original local appropriations finally approved in each such district so served to the sum total of all such original local appropriations finally approved. As soon as any unappropriated surplus shall accrue in the general fund account of any such school district after the beginning of such fiscal year sufficient for such reimbursement, before moving such surplus forward to the same fund account for the next succeeding fiscal year, the county treasurer shall deduct the amount of reimbursement so determined as aforesaid, transfer the same and place it to the credit of the general fund of the county.