Abstract: Organic matter (OM) is preserved as different occurrences in mudstones, which can affect the hydrocarbon generation process. However, little research has focused on hydrocarbon generation as a function of different occurrences of OM. This study collected a suite of mudstones in the Dongying Sag, Bohai Bay Basin, and conducted Rock-Eval VI pyrolysis after Soxhlet extraction and Na2S2O8 oxidation, aiming to quantify the OM with different occurrences and figure out the contributions of each occurrence of OM to the hydrocarbon generation. There are three types of occurrences of OM: soluble organic matter (SOM), mineral-bound organic matter (MOM), and particulate organic matter (POM). MOM is the most abundant among the three occurrence types of OM. SOM and MOM are the main hydrocarbon precursors, and their hydrocarbon contributions alternate with different kerogen types and layers. Additionally, MOM-contributed hydrocarbons are numerous at shallow depths; SOM-contributed hydrocarbons mainly occur at deep depths; and POM-contributed hydrocarbons change little with depth. These results demonstrate that MOM should be the main hydrocarbon precursor in shallow formations and that SOM is the main hydrocarbon contributor at deep depths.