The effects of Co, Ni, or Mo precursors having different oil solubility and oxidation state on the slurry phase hydrocracking (HCK) of vacuum residue (VR) was investigated at 673 K and 9.5 MPa H-2. X-ray diffraction and extended X-ray absorption fine structure spectroscopy were used to obtain structural properties of the dispersed catalyst. Under standard operating condition, the metal precursors were found to form nanoscaled dispersed particles of MoS2, Co9S8, and Ni3S2, with the following VR HCK performances in the order MoS2 > Co(9)Ss >> Ni3S2, based on the same metal loading of 0.113 mmol. Among the oil-soluble Mo precursors such as Mo-hexacarbonyl, -octoate, and -naphthenate, it was observed that Mo-octoate having an intermediate oxidation state forms the smallest particles of 5.8 nm in size and shows the best activity in the VR HCK. (C) 2018 Elsevier Inc. All rights reserved.