No standard biochemical parameters have been determined to define and grade agarwood, and the combination of its various constituent compounds can vary between different samples from the same tree.
Nevertheless, the value or grade of agarwood product has long been subjectively and comparatively graded by experts, based on colour, odour, specific gravity, and resin content, and prices can vary greatly for the same product depending on the grade (Naziz et al. 2019). Agarwood experts apparently can even differentiate between the scent profiles of agarwood oil (also known as oud oil) from wild-sourced stock from particular regions. The quality and value of extracts are dependent both on the skills of the manufacturer and the quality of the source product.
Agarwood grading in the marketplace often uses a lettering system (A to D) combined with descriptive terms (such as super, supreme, deluxe, +/-) and/or a numerical classification (1–5) to distinguish quality. There is no commonly accepted standard, even within individual countries or states, let alone across the industry. For example, it is possible to find agarwood graded as Super Deluxe, Super Double, Super, A, or oil graded as AAA, AA, A+, A, and A1 (Oud Oil Trading 2022) There are different grading systems in the various exporting countries. For example, Malaysia uses a 12-grade system, while Indonesia uses a 9-grade system. China has published its own guide for grading agarwood (Anonymous, 2017).
Various quantitative methods involving gas chromatography and mass spectrophotometry have also been used to distinguish among grades (e.g. Wang et al. 2021). But the industry still lacks a global grading standard for agarwood based on quantifiable indicators.