Another tip: Don’t fall for the “premium price” necessarily means better quality party line. Quality and purity are important, but you can get molecularly-distilled, mercury, PCB, Dioxin, Organochlorine-free, 3rd party tested-to-meet-label-claims fish oil for less than ten bucks per bottle of 400 (one gram) capsules… yet I have seen “fish oil gurus” selling the exact same thing for $50 to $60 claiming that everyone else’s products are “contaminated” and “inferior” in quality. If that’s true, then I’d like to see those products submitted to consumer lab for voluntary 3rd party independent analysis and head to head comparison on purity AND cost effectiveness. If they come out superior and cost effective, I will gladly publicize the results myself.

I can almost guarantee you that if these ridiculously overpriced fish oil brands were submitted to Consumer Lab and tested alongside the common and more cost effective brands they would NOT be shown to be superior. The kind of thing I'm talking about is overpriced stuff such as Biotest and the many so-called "pharmaceutical grade" fish oils and "ultra concentrated" fish oils on the market.

In terms of rancidity:

These highly processed fish oils will be JUST as prone to rancidity as ANY fish oil and they are quite likely to have a GREATER chance of being rancid. Fish oil begins the process of oxidation immediately. As soon as the fish body begins to be processed then the manufacturer is fighting the clock. The more complicated and prolonged the processing the greater the degree of oxidation. Most fish oil brands add an anti-oxidant such as Vitamin E to fish oil after processing. BUT this will not STOP the process of rancidification once it is begun. When it comes to fish oil, the faster and simpler the processing is the better.

In terms of yield:

It is a matter of opinion (and dubious opinion at that) whether more DHA or EPA respectively means a superior product. Consumer lab tests to make sure that products meet their label claims. Most products when touting an very high proportion of one constituent tend to fall short of the mark. This is especially true of DHA. However, this has nothing to do with QUALITY. Just quantity.

A moderately priced fish oil brand of the type Tom mentions, which contains the typical yield of DHA and EPA will meet your needs when it comes to a fish oil supplement. Do not fall for the swindlers trying to take your money. Most of the common store brands test well and very cost effective brands such as Puritan's Pride, Kirklands, and Berkley and Jenson will both meet your budget and give you are very dependable product.

For a more in-depth look see Fish Oil Quality