As part of the project Era Chair – Foodomics (Horizon Europe, GA-101186975 ), we are investigating the authenticity and quality of rosemary and bay laurel essential oils available on the Slovenian market. Using antioxidant assays, we analyzed samples of essential oils and assessed differences between them. By measuring the stable carbon isotope ratios, we examined potential adulteration in the oils. Our analysis identified possible cases of adulteration or the addition of other essential oils. This research supports producers and regulators in ensuring that label claims (e.g., “100% pure essential oil”) are accurate, thereby protecting consumers from misleading products.