In nature, agarwood scent profiles is differentiated based on their region of origin, the botanical species, age of infection and the infected area (stem vs body vs root vs heartwood vs bark).
Aquilaria is an interesting and special species, especially when infected for its commercial, cultural value. There are circa 49 different types of Aquilaria which some of them are cultivated, producing agarwood: Crassna, Malaccensis, Sinensis, which again having different scent profile in terms of woodchip and Oud oil. Click here for the full list
The order of the countries would be random. Each of us perceives scent differently and tend to have our own preferences. There is no superior of one to another.
To make it simple, only primary notes will be mentioned
Vietnamese Oud: Sweet, Spicy, slightly bitter, and herbal. These traits are perfect for heating which are the main ingredient for Japanese Premium Agarwood Incense. On the left: Wild vs On the right: Cultivated.
Cambodian Oud: Super Sweet, cinnamon, dried fruits, earthy, very stunning scent, you could sit and enjoy it for hours.
Indian Oud: I have not experienced it before personally, but it was described as rich, sweet, spicy and woody
Thai Oud: If you are into Oud, there are several well-known distillers which highly appreciate Thai Oud for "heady aroma with sweet undertones and earthy overtones".
Malaysia Oud. Most of the Oud business here was run by people from Yemen. Due to a high demand of its Oud, and short in supply, it is extremely hard to obtain pure Oud here, in term of quality. I experienced a small sinking piece from Malaysia, it is herbal, spicy, grassy, woody.
The majority is wild and there is limited plantation site in Indonesia. It offers complex notes: flowery, creamy sweet, slightly sour, very rich, spicy and woody. Below are two branches of Borneo agarwood
The cultivation and distillation play vital part in Oud scent profile
What do you think about
b) compared to b
As cultivation technique is confidential as well as distillation. Different suppliers will have different Oud oil and if they have multi plantation site which means different region, their own product would be different too.
It might be hard to know the difference in woodchip but it is very distinctive in Oud oil. The difference is clear. Here is the explanation by Kyarazen