MADRID, Nov 20 (Reuters) - In Spain, the world's biggest olive oil producer, supermarkets are locking up bottles of the staple cooking oil as prices surge and theft increases.

One-litre bottles of extra-virgin olive oil are selling for as much as 14.5 euros ($15.77) in some supermarkets, propelling olive oil into the category of products retailers fit with security tags, alongside spirits, cosmetics and appliances.

"We are seeing a major surge in shoplifting," said Ruben Navarro, the CEO of Tu Super supermarket chain, which operates 30 stores in Spain's Andalucia region. "Olive oil has become an ideal product for them to steal."

Olive oil prices, now officially at 8 euros a litre, have surged by 150% over the past two years in Spain as a scorching drought in the south has dented the olive harvest. Organised criminal gangs are stealing the oil to resell, Navarro said.

Since September, Tu Super has been chaining large 5-litre bottles of olive oil together and padlocking them to shelves to prevent theft.

"It is a crazy, extreme measure, but it has worked," Navarro said.

Tu Super is not the only one tightening security: in some Carrefour and Auchan supermarkets in Madrid, one-litre bottles are fitted with security tags that have to be removed by staff.

STC, a Spanish company providing anti-theft solutions to retailers, saw a 12-fold increase in orders this summer from supermarkets for devices to protect olive oil bottles, managing partner Salvador Canones told Reuters.

Spanish police have also uncovered thefts of olive oil from mills and in October arrested two people as part of an investigation into the theft of 56 tonnes of extra virgin olive oil.

Families in Spain typically buy olive oil in bulk for cooking. Among the world's biggest consumers of olive oil, they have already significantly cut back: sales volumes of extra-virgin olive oil fell by 17% in the 12 months to September, according to NielsenIQ.

While thefts of olives and oil have increased especially, the measures by supermarkets also reflect a broader shoplifting surge. Spain's top business organisation, CEOE, said there was a 30% increase in repeated thefts targeting retailers in 2022, and a further 12% so far in 2023.

In Spain, thefts of items worth less than 400 euros are not punished unless it is a repeat offence.

Navarro said thieves are taking advantage of lower numbers of staff in stores and shoplifters' often abusive behaviour towards workers is exacerbating the labour shortage.

"Our own workers live in fear after the robberies... some of them even end up resigning from their jobs," he said. ($1 = 0.9195 euros) (Reporting by Corina Rodriguez, Editing by Helen Reid and Elaine Hardcastle)