The defence ministry budget for 2016, which was presented in parliament on Tuesday, sets aside €25 million ($27 million) to buy four reconnaissance drones and two ground stations.
The entire five-year drone program has a budget of €171 million.
The defence ministry has selected the bid from privately owned US firm General Atomics, which has a teaming agreement with Spanish engineering firm Sener, to supply it with four Reaper drones, a ministry spokesman said.
"This type of equipment is necessary in operations today," he added.
The Reaper, which had a wingspan of 20 meters (66 feet), is already used by Britain, France and Italy and has been ordered by the Netherlands. The United States fly armed Reapers in combat zones but Spain only wants an unarmed version of the unmanned aerial vehicle (UAV).
The European defense industry does not produce reconnaissance drones like the Reaper, which is capable of flying 24 hours non-stop and can reach a maximum altitude of 13,700 meters (45,000 feet).
Germany, France and Italy decided in May to spend 60 million euros on a technical study for a European drone project proposed by Airbus, France's Dassault and Italy's Alenia Aermacchi of the Finmeccanica group.
"The Spanish defence ministry is interested in the development of a European project," the spokesman added.