Miss. Code Ann. § 27-31-19

There shall be exempt from all ad valorem taxes now levied or hereafter levied by the State of Mississippi, or any county, municipality, levee district, school, or any other taxing district within the state, all oil, gas, and petroleum products, whether produced within or without the state, which oil, gas or petroleum products are owned by a person, firm, or corporation operating a refinery for the refining of oil, gas or petroleum products in the state, and either (1) are in transit to or situated at an in-state refinery for refining thereat; (2) are in the process of being refined at such a refinery; or (3) have been refined at such refinery and are still owned by or in the hands of the refiner. Such exemption shall also extend to such oil, gas and petroleum products owned by any corporation controlled by, under common control with, or controlling such a refiner; provided, however, that the exemption afforded by this section shall not extend to those finished petroleum products incident to regular, normal, and customary marketing operations held in temporary storage at marketing bulk plants outside refinery property, including storage facilities from which a finished product is marketed in the state and from which a finished product is shipped out of the state for marketing, or at retail service stations.