.nif (short for Net Immerse File) files are files that can hold physical models, nodes and animations. They are used by the Net Immerse/Gamebryo Engine and can be found in a variety of games, such as Zoo Tycoon 2, Oblivion and Wildlife Park 2. They can be edited using hex editors, Nifskope, Autodesk 3DS max, Gmax and blender. The .nif format was used from the base game til African Adventure. From Marine Mania onwards, models are saved as .bfb files. However, some test nifs were remaining.