We conducted hydrous pyrolysis experiments using a Dickson-type experimental setup (Dickson et al., 1963) under elevated p-T conditions (p = 20-25 MPa, T = 150, 200 and 250°C). These experiments were designed to assess changes in the molecular composition of dissolved organic matter (DOM) produced by abiotic reactions at temperatures representative of the deeper parts of the Nankai Trough subduction zone. As reference, the Nankai Trough porewater sample C0023A-72R-1 WR, 20.0-52.0 cm, 370VHIW3 (89°C) was used. For data processing, the Bruker Compass DataAnalysis 4.3 software (Bruker Daltonics) and ICBM-OCEAN (Merder et al., 2020) were used for visualizing, processing and interpreting mass spectrometry data. The FT-ICR-MS generated data of all experiments (T = 150-250°C) and the in-situ sample (T = 89°C) were processed via ICBM-OCEAN.