Omega-3 fatty acids in fish oil are available in 3 forms
A great majority of concentrated omega-3 fish oils in the market are in the EE form, whereas a limited number of omega-3 fish oils are in the super-absorbable and bioavailable rTG form. This is attributed to the extra costs involved in re-esterifying ethyl ester fish oil back to rTG form, and it is not surprising that rTG fish oil is more expensive than EE fish oil.
¥Prostaglandins Leukot Essent Fatty Acids.83(3): 137-141 (2010)
In brief, look for re-esterified triglyceride (TG) rather than ethyl ester form of fish oil for better absorption, utilization, stability and potency.