Spain’s top court has rejected seven appeals against oil exploration in the Canary Island waters, giving the go-ahead for exploration there.
In 2012, the government reinstated a decade-old permit to prospect for oil off the coast of Fuerteventura and Lanzarote, but it was then put on hold following challenges.
Environmentalists and local authorities had appealed on the grounds of the impact prospecting could have on tourism.
Spanish energy firm Repsol may now be able to start exploring.
It has said exploration could start in the third quarter of this year with commercial drilling potentially taking place in 2019.
Campaigners criticised the decision.
Ricardo Aguilar, the research director of Oceana in Europe, who was an expert witness during the case, said: "The Canary Islands' deep-sea ecosystems are unique and they sustain species that are vital for the tourism and fisheries in the area. It is irresponsible to destroy these habitats in a few years to facilitate the extraction of a finite and highly polluting energy resource."
He added it was a “disgrace how the government is handing out exploration permits that benefit just a few people, while putting the rest of Spain in danger of losing countless essential and extremely fragile habitats."
Oceana said it had documented 82 protected marine species during an expedition it conducted in the oil blocs.
Meanwhile, Scottish oil explorer Cairn Energy says it has licences for exploration in the Gulf of Valencia near Ibiza and is waiting for the government to decide on its environmental impact assessment which will determine if it can continue.