Omega-3 polyunsaturated fatty acids (PUFAs) supplements are widely used in recent years due to their known potential beneficial effect in a variety of neurological disorders and cardiovascular disease. Commercially available omega-3 dietary supplements are known to contain the desired fats, as well as harmful oxidized lipids, derived from the undesired oxidation processes of omega-3. Our study tested 14 most popular commercial brands of fish oil derived PUFAs and 3 non-fish (plant or algae)-derived PUFAs, available in Israel in 2016. The objective of this study was to determine the essential fatty acids content, as well as three known oxidation markers in omega-3 dietary supplement. Our data reveals for the first time that high levels of oxidized saturated fats are found in common n-3 PUFAs dietary supplement commercially available in Israel (fish, plant and algae-derived), as was recently reported in other countries, and may interfere with their intended biological benefits.