The oligomeric products from lignin depolymerization represents a bottleneck issue in biomass conversion. Fundamentals behind its generation, identification, and further valorization are all to be significantly disclosed/addressed before we can expect the conversion of lignin in an efficient style. This review manuscript focuses on this important issue, briefly summarizes the three major depolymerization approaches of reductive catalytic fractionation, oxidative catalytic fractionation, and pyrolysis. The main identification techniques regarding the oligomeric products characterization are also highlighted. In general, this is a timely review paper on the important topic of biomass conversion. However, several important problems should be addressed before it can be considered for publication.

1. Three depolymerization methods are summarized in the text, however, other important progresses are not included. For instance, redox-neutral strategy (JACS 2010, 132, 12554; Angew. Chem., Int. Ed. 2015, 54, 5859; etc.). Particularly, such a strategy can depolymerize lignin into produce lignin oil (most are oligomers) in yield higher than 80% even using raw biomass as the substrate (ACS Catal, 2019, 9, 4441; Green Chem. 2020, 22, 33; etc.). Relevant progresses should be included in the text and illustrated in Figure 2. Meanwhile, I also suggest show more details in pathways of Figure 2.
2. Besides Maldi-TOF, LTQ Orbitrap Elite can also be employed to identify the oligomers (ChemSusChem, 2016, 9, 3220; 2017, 10, 523), which could give a comprehensive molecular weight distributions of the depolymerized products along with molecular weight of each oligomer.
3. In addition, newest appeared protocol for analyzing lignin dimers by Supercritical Fluid Chromatography should be mentioned (Turner et al. Analysis chemistry, 2023, https://doi.org/10.1021/acs.analchem.2c04383); and 31P NMR is a powerful tool to identify the hydroxyl groups’ distribution and determine the aliphatic, phenolic, and acidic hydroxyl contents in lignin and oligomers (Xie et al. ChemCatChem, 2017, 9, 1135). I believe they all deserve introduce in the text.
4. Regarding Figure 3, many literatures have characterized the average molecular weight by TOF and GPC, what is the criterion of literature selection? In my opinion, they should select representative literatures of all the major depolymerization methods. The same issue in Figure 4, why select these 7 refs ?
5. Part 4 discussed further valorization options for the oligomers, I suggest adding two options: 1) Conversion of lignin and oligomers to value-added chemicals, such as N-participated depolymerization strategy reported by different researchers (Chem. Sci. 2015, 6, 4174; Nat. Catal. 2018, 1, 82; ChemSusChem, 2020, 13, 4660; Angew. Chem. Int. Ed. 2021, 60, 20666; Nat. Commun. 2022, 13, 3365; Angew. Chem. Int. Ed. 2022, e202206284; etc). 2)modification of lignin and lignin oligomers into value-added materials (such as Chen et al. Nat. Commun. 2022, 13, 5508; Sipponen, et al. Mater. Horiz. 2020, 7, 2237).

The authors properly addressed all my concerns, and the manuscript can be accepted as is.