Evening Primrose Oil
INCI Oenothera Biennis Oil. CAS 90028-66-3; EC 289-859-2, as CosIng gives them. Also: Oenothera biennis seed oil, EPO, Evening primrose seed oil.
Published values
| Saponification value | 187.35 mg KOH/g |
| Used by the calculator | 187.4 mg KOH/g (typical) |
| SAP for NaOH | 0.1336 g/g |
| Iodine value | 125–165 g I₂/100 g |
| INS (SAP − IV) | 42 |
| Melting point | — |
| Unsaponifiable matter | 3.2–5.2 % |
Soapmaking books print about 0.136 g NaOH per g (median of 4 books), which agrees with ours to within 2 %.
A bar made of 100 % Evening Primrose Oil
Conventional qualities summed from the fatty-acid groups; a single-oil bar is a reference point, not a recipe.
How much lye
| Oil | NaOH | KOH |
|---|---|---|
| 500 g | 63.4 g | 89.0 g |
| 1 kg | 126.9 g | 178.0 g |
| 1 lb (454 g) | 57.6 g | 80.7 g |
| 2 lb (907 g) | 115.1 g | 161.5 g |
For this oil alone at 5 % superfat, with pure sodium hydroxide (NaOH) or pure potassium hydroxide (KOH); in brackets, across the published range of its saponification value. KOH is usually sold at 90 %: divide by 0.9. For a whole recipe, open the calculator.
Fatty-acid profile
Saturated : unsaturated 8 : 92
| Fatty acid | Published range, % | Used | |
|---|---|---|---|
| Caprylic acid | C8:0 · saturated | 0.2 | 0.2 |
| Lauric acid | C12:0 · saturated | 0.3 | 0.3 |
| Myristic acid | C14:0 · saturated | 0.1 | 0.1 |
| Palmitic acid | C16:0 · saturated | 5.2–7.2 | 6.2 |
| Palmitoleic acid | C16:1 | 0.1 | 0.1 |
| Stearic acid | C18:0 · saturated | 0.4–1.6 | 1.0 |
| Oleic acid | C18:1 | 6.6–14.2 | 10.4 |
| Linoleic acid | C18:2 | 70.7–70.8 | 70.8 |
| α-Linolenic acid | C18:3 n-3 | 0.2–0.3 | 0.3 |
| γ-Linolenic acid | C18:3 n-6 | 7.1–13.7 | 10.4 |
| Arachidic acid | C20:0 · saturated | 0.1–0.3 | 0.2 |
| Gadoleic acid | C20:1 | 0.2 | 0.2 |
| Behenic acid | C22:0 · saturated | 0.1 | 0.1 |
Where these numbers come from
Table 1 oil content (16.9 / 16.7 %), Table 2 unsaponifiable matter (3.2 / 5.2 %), Table 3 fatty-acid composition for the 2023 and 2024 harvests.
Table 1 row 'Evening primrose oil': iodine value 125-165, saponification value 187.35, unsaponifiable 1-3 %, density 0.91-0.93 (review's reference [88]).
Fatty acids and unsaponifiable matter are from the PRIMARY open-access paper (Pharmaceuticals 2026) on Bulgarian Oenothera biennis seeds from two harvest years: Table 3 gives, for 2023 / 2024 respectively, palmitic 5.2 / 7.2, stearic 1.6 / 0.4, oleic 14.2 / 6.6, linoleic 70.7 / 70.8, alpha-linolenic 0.2 / 0.3, GAMMA-linolenic 7.1 / 13.7, arachidic 0.3 / 0.1, gadoleic 0.2 / not detected, behenic 0.1 / nd, palmitoleic 0.1 / nd, caprylic nd / 0.2, lauric nd / 0.3, myristic 0.1 / 0.1, margaric C17:0 0.1 / 0.1, heptadecenoic C17:1 0.1 / 0.1, nervonic C24:1 nd / 0.1 (% of total). The min/max in this record are the two-year spread; acids detected in only one year are given as 'typical'. Evening primrose oil's defining acid, gamma-linolenic acid (GLA, C18:3 n-6, 7.1-13.7 % here), is stored under its own key 'gammaLinolenic', separately from 'linolenic' (alpha-linolenic only). Unsaponifiable matter measured 3.2 +/- 0.1 % (2023) and 5.2 +/- 0.1 % (2024), Table 2; the review below quotes 1-3 % and another Foods 2025 paper (PMC11765098) cites 1-2 % from literature, so commercial oils are usually lower than this record's range. Saponification value (187.35 mg KOH/g) and iodine value (125-165 g I2/100 g) were NOT measured in the primary paper; they are transcribed from Table 1 of the Frontiers in Nutrition 2026 systematic review of cold-pressed oils (row 'Evening primrose oil', attributed there to its reference [88]; the same row lists density 0.91-0.93). Treat the SAP as a literature typical value, not a specification. Melting point not given (liquid oil). INCI name from CosIng. INCI: The CosIng name has no plant part in it — "Oenothera Biennis Oil", not "... Seed Oil" — though the oil is pressed from the seed.
This record is part of the open ingredient database (ODbL), which you can download as CSV or JSON. Found an error or a better primary source? Corrections with a link to the document are welcome at support@soapformulator.com.