Ask the seller a certificate. A good fish oil if you have this document, it must contain information about the raw materials (or cod liver oil, or polar salmon, seal or subcutaneous fat or a coating fat of whales, etc.), as well as an official confirmation of absence in the product of toxins and other data.
Read the label. If your goal is to buy a useful addition to his diet to fill him in polyunsaturated fatty acids omega-3, pay attention to the product name. It needs to be called "Medical cod liver oil" (not veterinary, food, etc.).

On the label or packaging of fish oil should contain proportion of polyunsaturated fatty acids omega-3 (%fatty acids of the total weight of the formulation). It is considered that fats should not be less than 15%, although some manufacturers this proportion can reach 25 and 30%, and even more. Standards do not exist.

If you read on the label that the fish oil prepared by the method of molecular differentiation can safely take this product. However, it may be more expensive, but you can be sure in high quality of this Supplement. The fact that this process found really useful omega-3 fats.
Few buyers pay attention to the fact that on some products written "Fish oil" and other "Fish oil". Meanwhile, there is a difference, and it is the percentage content of omega-3.

Fish oil is produced mainly from the liver of cod fish. There are a lot of vitamins A, D and E, but low in omega-3. For the production of fish oil are used by muscle fibers of fish, it contains large amounts of omega-3, but less vitamins. The choice depends on goals of treatment.
If you choose fish oil capsules, pay attention to the substance from which they are made. Some manufacturers use gelatin of animal origin, other fish gelatin. In the first case, the product is cheaper. Also look at the weight of the capsule. Based on the weight of one capsule, you will count your daily intake (for an adult it 650-100 mg).
If your choice is fish oil "on tap", see below the bottle was of dark glass and tightly sealed, because when exposed to light and oxygen omega-3 is quickly oxidized and decomposes. Use of such a product will not.
Pay attention to the manufacturer. Experts believe that the best fish oil produced in Norway, a country which is the main supplier of this product to the world market (over 80%). Of domestic products traditionally valued fish oil from Arkhangelsk and Murmansk fish combine.
Don't forget to look at the date of manufacture. The usual shelf life of fish oil is 2 years. Some manufacturers put a lower or higher shelf life. Always match the designated shelf life from date of manufacture of the product.