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Oud oil is mainly made by hydro-distillation, where soaked, ground agarwood is boiled in water and the oil collected from the vapour. Steam distillation passes steam through the wood instead, and supercritical CO2 extraction uses pressurised carbon dioxide. CO2 is faster and gives more oil, while hydro-distillation remains the most popular. Yields are very low, often around 0.1 percent of the wood's weight.
- Agarwood is usually soaked for days or weeks before distilling.
- In one study, a 14-day soak gave about twice the oil of a 6-day soak.
- Hydro-distilled oil is rich in sesquiterpenes and usually low in chromones.
Resin content, covered in agarwood resin content, sets how much aromatic material a piece of wood holds. How that material is extracted decides a great deal about the finished oil. Three methods dominate, and they do not give interchangeable results from the same wood.
| Method | How it works | Trade-offs |
|---|---|---|
| Hydro-distillation | Wood boiled in water, oil collected from the vapour | Traditional and most common; slow, low yield |
| Steam distillation | Steam passed through the wood | Similar principle, different contact between heat, water and wood |
| Supercritical CO2 | Pressurised CO2 used as a solvent | Faster and higher yield; captures a broader range of compounds |
Three methods, one material
All three start from resinous agarwood, usually chipped or ground to expose more surface. They differ in how heat, water and solvent reach the wood, and that changes which compounds end up in the oil, how much oil is recovered, and how long the process takes.
Hydro-distillation: the traditional method
Hydro-distillation is the traditional method and still the most widely used, including in Malaysia's agarwood industry, according to researchers there. The wood is soaked, then placed in a still with water and boiled. Steam carries the volatile oil into a condenser, and the oil separates from the water, the hydrosol, and is collected. The process is slow and energy-intensive: one comparison of methods reported hydro-distillation taking around seven days, against about four hours for supercritical extraction.
Because it relies on long boiling, hydro-distillation favours the more volatile compounds. A review of agarwood oil chemistry found hydro-distilled oil tends to be rich in sesquiterpenes and usually contains few or no 2-(2-phenylethyl)chromones, and that long high-temperature exposure can lose some lighter aromatics. That is part of why hydro-distilled oil has the character it does.
Why soaking time matters
Before distilling, agarwood is usually soaked in water for days or weeks, sometimes with deliberate fermentation, to soften the wood and help release the oil. Soaking time is one of the variables a distiller controls most directly, and it measurably changes the result. In a 2020 laboratory study, wood soaked for 14 days gave about 0.135 percent oil by weight, roughly twice the 0.0625 percent from wood soaked for 6 days. Another study cited there found a 14-day soak gave the highest yield, with yields falling when soaking went longer.
Distillers also describe soaking as shaping the scent, not just the yield, which is one concrete reason two oils from comparable wood can smell different. That is a widely held trade view rather than something measured in published studies.
Want to know what is happening to the resin chemistry in the first place?
How agarwood resin formsSteam distillation
Steam distillation works on the same principle but passes steam through the wood rather than boiling the wood in water. The different contact between heat, water and wood can change the oil's character. Which countries favour which method varies by producer, and we have not found reliable evidence for neat country-by-country rules.
Supercritical CO2 extraction
Supercritical CO2 extraction uses carbon dioxide held under pressure in a state between gas and liquid as the solvent. It can work at lower temperatures than boiling, which avoids long heat exposure, and it is much faster. Comparisons of methods for gaharu oil found supercritical extraction gave a higher yield in a much shorter time than hydro-distillation, steam distillation or solvent extraction.
Higher yield is not the same as a better oil. CO2 extraction pulls a broader range of compounds, including heavier, less volatile ones, so its oil has a different profile from a traditional hydro-distilled oil. Many oud enthusiasts prefer the character of traditionally distilled oil, while others value CO2 extracts for different qualities. The choice is a trade-off, not a hierarchy.
How little oil wood gives
Yields are strikingly low. The laboratory figures above, around 0.06 to 0.14 percent, mean roughly 0.6 to 1.4 grams of oil per kilogram of wood. The other study cited there reported 2.5 grams of oil from 25 kilograms of agarwood, about 0.1 grams per kilogram. On those figures, a single tola of oil, about 12 ml, could take anywhere from around 8 to over 100 kilograms of wood, depending on resin content, soaking and method. That is the starting point for why oud oil prices vary.
What "fractions" mean
Because a distillation can run for a long time, oil collected early can differ from oil collected later in the same run. That is the genuine basis for "first fraction" and similar labels. Whether a given label reflects a careful, tracked separation or simply oil drawn in sequence varies by seller, and buyers usually cannot check it. As covered in Middle Eastern oud grading, treat it as a description rather than a standard.
How we checked this. Yields, soaking results and timings come from the studies listed below. We corrected the draft's distillation time and removed country-by-method claims and comparative compound counts we could not confirm.
Sources
- Abdul Rahim, A. F. et al. (2020). Microwave-assisted hydrodistillation of Aquilaria subintegra. Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 72(2), 1 to 12.
- FAO AGRIS. Comparison of extraction methods for gaharu oil (2010 seminar paper, Universiti Putra Malaysia).
- Chen, X. et al. (2022). Chemical composition and potential properties in mental illness of agarwood essential oil: a review. Molecules, 27(14), 4528.