Adulteration of essential oils (EOs) is a common and unethical practice that affects both consumers and honest suppliers and harms market integrity. Despite the awareness of this problem, scarce scientific studies are described in the scientific literature. Therefore, 55 samples of lavender EOs were purchased and extensively analyzed to the trace levels, including chromatographic profile, quantitative analysis, and chiral profile. Of the 51 samples labeled as Lavandula angustifolia, 51 % were genuine, 6 % were cheaper lavandin EO, 14 % were fortified with synthetic additives and over 29 % of the samples were adulterated with both lavandin EO and synthetics. Usually, adulterated EOs were cheaper than genuine products, still some expensive products were also falsified. The most common synthetic adulterants were synthetic linalool and linalyl acetate, 3,5,5-trimethylhexyl acetate, α-terpinyl acetate, and dipropylene glycol. Only four of the studied samples were diluted with a medium not fully visible in the recorded GC profile. Industry standards were assessed to eliminate adulterated EOs and ISO 3515 was found to be impractical and too strict, but Ph. Eur. demonstrated its efficiency in eliminating adulterated samples without rejecting many genuine ones.PCA enabled the differentiation of lavender EOs containing synthetics from those of purely natural origin, and in the latter group, to distinguish L. angustifolia from lavandin. Some samples had an unusual composition suggesting that they were artificial blends of synthetics and some terpene fractions of non-lavender origin.This is the first such extensive study of adulteration of lavender EOs, regarding both the number of commercial samples as well as implications on their biological activity. The adulteration via dilution influenced the antimicrobial activity of the essential oils. In conclusion, adulteration is a significant problem in the market, and a large share of products on the market is somehow counterfeited, not only the cheapest products.