Five small explosive devices detonated Friday at Madrid petrol stations after a telephone warning from the armed Basque separatist group ETA, reports said.
There were no injuries and only minor damage, Interior Ministry officials said.
The explosions occurred at petrol stations on the outskirts of the city as travellers left for the weekend.
Earlier, the Basque newspaper Gara said it had received a call from a person speaking on behalf of ETA who said five explosive devices had been placed at gas stations along major highways leading out of Madrid.
ETA has been blamed for more than 800 deaths since the late 1960s. It staged a string of small explosions in resort towns in northern Spain over the summer, causing slight damage and only a few minor injuries.