Related Rule
Spain
Practice Relating to Rule 108. Mercenaries
Section B. Status of mercenaries
Spain’s LOAC Manual (1996) included mercenaries in the section concerning persons not entitled to protection, stating:
They are neither considered civilians nor have the right to take a direct part in hostilities as combatants. The more important consequence is that to the extent that they take a direct part in hostilities, they shall not be entitled to prisoner-of-war status. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Publicación OR7-004, 2 Tomos, aprobado por el Estado Mayor del Ejército, Division de Operaciones, 18 March 1996, Vol. I, § 1.4.b.
Spain’s LOAC Manual (2007) states that mercenaries “are not entitled to prisoner-of-war status if they are captured”. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 1.4.