Flax oil products are on shelves everywhere and are competing against fish oil for 'numero uno' as the ultimate omega-3 fatty acid source. Whether flax is an actual contender, though, is a source of controversy.
From a fatty acid perspective, flax contains high amounts of alpha-linolenic acid (ALA), which the body first must convert to EPA (eicosapentaenoic acid) and docosahexaenoic acid (DHA) to achieve any benefit. Fish oil, on the other hand, presents readily available EPA and DHA. This isn't a problem, except that in order to derive equal nutrition from the fatty acids in flax oil you'd have to consume far greater amounts, possibly hundreds of times the amount.
Still, flax oil may provide at least some of the health-supporting benefits touted by fish oil– it may help maintain healthy cholesterol and blood pressure levels already in the normal range and support arterial health. And flaxseeds offer certain benefits that fish oil does not. For example, flax contains phyto-nutritious lignans and is high in fiber, protein, magnesium and thiamin. All things good for a balanced diet.