Evening primrose oil is highly valued for its high level of essential fatty acids. Its rich in omega-6 EFAs Linolenic Acid. Gamma Linolenic Acid and Evening Primrose Oil. Cold-pressing Oenothera Biennis seed can be done. Evening Primrose can also be used as a plant. This is how oil gets extracted. Sometimes. evening primrose oil can be mixed with carrier oils (often 10%).