Spanish energy firm Repsol began searching for oil Tuesday in the waters off the Canary Islands, a top holiday destination, despite objections from environmentalists and the local government.
"The drilling started today," a company spokesman told AFP.
Oil exploration vessel Rowan Renaissance started operating at dawn some 50 kilometres (30 miles) from the islands of Lanzarote and Fuerteventura, off the west coast of Africa, he added.
The prospecting is expected to last about 60 days.
Spain's Industry Ministry in August authorised Repsol to search for oil in the region at three locations at depths ranging from three to seven kilometres.
The company estimates its chances of finding oil in the region are of 17-19 percent and plans to invest 350 million euros ($438 million) in the oil exploration.
It says the search will create badly needed jobs in the archipelago which has an unemployment rate of 34 percent, compared to 24 percent for all of Spain.
But locals and green groups oppose the oil exploration. Residents fear Repsol's prospecting will harm local flora and fauna such as dolphins and disrupt the tourism industry that is vital to the area's economy.
They have tried to stop the exploration effort going ahead.
A Greenpeace activist was hurt Saturday in a confrontation with the Spanish navy that intervened during fresh protests against the exploration project.
The propellor of a boat cut and broke a 23-year-old Italian woman's leg after she fell overboard during the dawn clash, according to Spanish authorities.
The Spanish defence ministry said the navy believed the activists were trying to board the Rowan Renaissance, and had moved in to halt three Greenpeace boats. However, the activists say they intended to carry out a "peaceful protest."
The clash with the Spanish navy vessels on Saturday came just one day after rallies against the oil exploration were held across the Atlantic archipelago, whose beaches are a popular draw for foreign tourists from Britain, France and elsewhere.
Fearing a loss to the tourism industry, the regional government of the Canary Islands called a referendum to allow residents to vote on it, but the national government in Madrid has blocked that in the courts.
Spain imports nearly 80 percent of its energy and the central government argues it can no longer afford the luxury of holding back business or wasting natural resources.
The Canary Islands are Spain's third most popular destination after Catalonia and the Balearic Islands.
The archipelago received 10.6 million foreign visitors last year, 17.5 percent of the total number of visitors to Spain.