This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Nature Publishing Group. ; One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate of the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. Our results point at a large Fermi surface consistent with Luttinger?s theorem and a strongly enhanced carrier effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition. ; This work is supported by the EPSRC through grant EP/K012894/1. SF acknowledges support by the ERC and the Alexander von Humboldt foundation. PR acknowledges funding from the Cusanuswerk and the EPSRC. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by NSF DMR-1157490 and the State of Florida. SWT, WAC, and DEG were supported in part by DOE NNSA SSAA DE-NA0001979.