By using other oils and additives, fully or as a mix. It can also involve faking the label promises of “extra virgin”.

Examples:

https://www.theguardian.com/world/article/2024/jul/29/olive-oil-fraud-mislabelling-cases-record-high-eu

https://www.oliveoiltimes.com/business/europe/top-italian-police-official-explains-how-olive-oil-fraud-works/133568

https://www.foodnavigator.com/Article/2025/05/08/olive-oil-a-major-target-for-food-fraud/

How to spot fake olive oil: https://www.youtube.com/watch?v=yZ1dKZfi1E8 (it’s not easy)

A short documentary about olive oil fraud: https://www.youtube.com/watch?v=cOjhqfld3X8