N.M. Stat. § 7-16A-6
A "special fuel inventory tax refund" is established measured by the quantity of gallons of special fuel in the possession of a supplier or bulk storage user on the day in which a decrease in the special fuel excise tax rate is effective. The refund event is the existence of an inventory in the possession of a supplier or bulk storage user on the day prior to the day in which a decrease in the special fuel excise tax rate is effective. The refund is to be calculated by determining the difference between the special fuel excise tax rate imposed on the day prior to the day in which the special fuel excise tax rate is decreased, subtracted from the special fuel excise tax rate imposed on the day in which the special fuel excise tax rate decrease is effective, expressed in cents per gallon. The refund rate so determined is then multiplied by each gallon in inventory as determined under Section 5 [7-16A-5 NMSA 1978] of the Special Fuels Supplier Tax Act.
NMS § 7-16A-6