Ala. Code § 40-15-4
The tax imposed by this chapter shall be paid and the return required by Section 40-15-3 shall be filed on or before nine months after the decedent's death and shall be paid by the personal representative to the Department of Revenue; provided, that where the Department of Revenue finds that the payment on the due date of any part of the amount due would impose undue hardship upon the estate, the Department of Revenue may extend the time for payment of all or any part, not to exceed 10 years from the original due date. In such case the amount or amounts in respect of which the extension is granted shall be paid on or before the dates thus fixed, unless further extended within said limitation as to time. If the time for payment is extended, there shall be collected, in addition to the tax, interest thereon at the legal rate from the original due date of the tax to the date of payment. The Department of Revenue may, in its discretion, accept such security as it may approve for the deferred payments or may release any part of remainder of the estate from any claim or lien for the payment of the tax.
Ala. Code § 40-15-4 (1975)