A process for producing a crude oil having lowered unsaponifiable mattercontent and/or ester-type sterol content and comprising a highly unsaturatedfatty acid as a constituent fatty acid, characterized in that a microorganismcapable of producing a fat or oil comprising an unsaturated fatty acid as aconstituent fatty acid is cultured in a medium containing a nitrogen sourceconcentration of 2 to 15% within a culture tank equipped with an agitationimpeller satisfying the requirement that the ratio of the diameter ofagitation impeller (= d) to the inner diameter of the culture tank (= D) isd/D = 0.30 to 0.6.
