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

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 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.

Testing of fish oil supplements in Bahrain found that more than half had high levels of early-stage oxidation markers, but few showed signs of advanced spoilage; however, about one in three still exceeded safety limits for total oxidation.