Spain is already the world's largest olive oil producer but now it's looking to a very different kind of oil to pull it out of economic decline: petroleum.

The discovery of two significant offshore deposits, and prospects for fracking in many areas, have triggered a black-gold rush, with demand for exploration permits up 35% since 2012.

A report published this week by Deloitte says the oil industry could create 250,000 jobs and constitute 4.3% of GDP by 2065. The report is based on an estimate of 2bn barrels of oil and 2.5bn cubic metres of gas.

The oil companies estimate that the deposits in a series of oilfields off the Canaries, the latest of which was confirmed last week, amount to 500m barrels of crude.

Deloitte predicts that Spain could become a gas exporter by 2031 while producing 20% of the oil it consumes.

With 6 million people unemployed and an economy that shows only feeble signs of recovery, the Spanish government seems ready to brush aside environmental concerns and give the green light to the oil companies. These are led by the Aberdeen-based oil and gas exploration company Cairn Energy and the Anglo-Turkish firm Genel Energy, headed by the former BP boss Tony Hayward. So far, 70 licences have been granted to explore both shale gas and conventional resources.

The main offshore deposits lie between Lanzarote, in the Canary Islands, and Morocco, and in the Bay of Valencia, close to Ibiza. As both the Canaries and Ibiza are places of great natural beauty whose principal industry is tourism, there is intense opposition to the plans.

Opposition is so fierce in Ibiza that the Eivissa diu no (Ibiza says no) movement has succeeded in creating a united front across the entire political spectrum, taking in environmental groups and hoteliers, and has won the support of celebrities such as Kate Moss, Sienna Miller, Fatboy Slim and Paris Hilton, who wrote on Instagram: "Don't let them ruin one of the most beautiful islands in the world." The record producer and rapper Puff Daddy described the plans as "a disaster on every level".

Last month, more than 20,000 people marched in Ibiza (which has a population of 132,000) to oppose the exploration, and thousands signed a petition to the European commission demanding a halt to sonic exploration that was producing 250-decibel booms every 10 seconds, day and night, over a period of three months. As well as breaking the safe limit, of 180 decibels, the booms damage fisheries and bird life, the protesters say.

David Sala, a spokesman for the Ibiza says no movement, said: "Just because we have the technology to exploit nature, we can't continue to use technology that destroys the environment and, by extension, ourselves."

Paulino Rivero, president of the Canary Islands regional government, wrote to the Spanish prime minister, Mariano Rajoy, last month telling him that he plans to hold a referendum on the issue, posing the question: "Do you agree with the oil exploration off the coast of our islands authorised by the multinational Repsol?"

The Spanish government's only response was to remind Rivero that referendums are illegal under the constitution.

Antonio Martín, president of the Spanish oil exploration association, said: "When we talk about exploration and production of hydrocarbons in Spain, we are talking about creating employment [and] wealth for the country and improving our commercial standing in the world."

Spain depends on imports for 99% of its oil and gas needs. Aside from some coal mines in the north, the country, has never been blessed with energy resources.

It has a highly developed hydroelectricity industry – only China and the U.S. have built more dams – and its ageing nuclear power stations meet 20% of demand.

Until recently, it was investing heavily in renewables. Wind power now provides 20% of the grid and solar 3%, but the current government has lost its enthusiasm for renewables, and has made drastic cuts in subsidies.

The most promising areas for shale gas are in the north, principally the Basque Country, Asturias and Cantabria; the first explorations have begun, in Asturias and Castilla y León.

Several regional governments have outlawed fracking but last year the central government used its overall majority to pass legislation that overrules regional administrations on the issue.

"The minister has to defend the interest of Spain as a whole, and the regional presidents have every right to defend their interests," said Enrique Hernández Bento, who is minister for both energy and tourism. "The government will support these explorations as long as they comply with legal and environmental requirements."

The organisation Shale Gas España says: "This won't be a panacea that makes Spain self-sufficient." But, it says, fracking will allow Spain to be 60% rather than 80% dependent on conventional gas.

An independent consumer association says that if enough shale gas is found, the cost to the consumer should fall. This could help offset the high energy prices Spaniards pay as result – the association claims – of the high investment in renewables.