In China, more expensive fish oil supplements are not consistently cleaner or safer than cheaper ones, as price does not reliably reflect how oxidized the oil is or whether it contains harmful metals.

In fish oil products sold in China, measurements of chemical oxidation do not reliably predict whether the oil smells fishy or rancid to consumers.

Fish oil supplements with higher concentrations of EPA and DHA tend to cost more, but paying more does not guarantee the product is less oxidized or more stable once you account for the actual EPA and DHA content.

In a study of fish oil products in China, most commercial capsules met quality standards for oxidation, but nearly all bulk industrial samples did not, showing that bulk fish oil is more likely to be degraded.

Fish oil supplements from countries other than New Zealand or Australia cost more but contain the same amounts of EPA and DHA and show similar levels of oxidation, meaning where they are made does not determine how good they are.