Annually, no later than thirty days after the delivery of its annual report to the governor and the legislative finance committee, the corporation shall return to the severance tax permanent fund an amount equal to the net excess of funds held by the corporation. For purposes of this section, “net excess of funds” means the return on investments to the corporation in the amount of dividends and interest actually received plus any capital gains actually realized, less the operating expenses of the corporation and less amounts reasonably reserved for losses.