Raids were carried out in both countries by the Guardia Civil and Carabinieri as part of the investigation also involving Europol.
Olive-processing cooperatives believed to be tampering with olive oil to increase profits were searched, The Guardian reports.
Guardia Civil officers are said to have discovered “a series of anomalies” while inspecting a lorry transporting olive oil in Ciudad Real region.
A criminal network set up to distribute adulterated olive oil on the global market was reportedly uncovered..
Spanish and Italian police said in a statement: “In Spain, they used a company that was linked to the acquisition of lower-category oils to make changes to cloudy and poor quality oils to turn them into virgin and extra virgin and then sell them by falsifying documents.
“They mixed cloudy oils – a sub-product of the olive oil producing process – with better quality olive oil so as to obtain the correct levels of fats and [other substances] to allow them to be sold. They also impeded traceability by not registering their companies’ oils.”
Police in Italy discovered a similar alleged falsification operation involving two important oil-processing companies.
The statement added: “Eight simultaneous searches were carried out in Spain and Italy and 11 people were arrested.
“As a result of the searches, more than 5,200 litres of market-ready, adulterated olive has been seized, along with €91,000 [£78,000] in cash and four high-end vehicles. A number of bank accounts have also been blocked.”
Prices of olive oils have been rising after European harvests suffered from drought and other poor growing weather for two successive years.