diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index 8ce9e7c9..360cadd0 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -159,6 +159,7 @@
     <Compile Include="FC01\ArcBDT.cs" />
     <Compile Include="FC01\ArcSCXA.cs" />
     <Compile Include="FC01\BdtTables.cs" />
+    <Compile Include="Fog\ArcDAT.cs" />
     <Compile Include="GScripter\ArcDATA.cs" />
     <Compile Include="Ism\ImagePNG.cs" />
     <Compile Include="Kid\ArcDATRAW.cs" />
diff --git a/ArcFormats/Fog/ArcDAT.cs b/ArcFormats/Fog/ArcDAT.cs
new file mode 100644
index 00000000..421de416
--- /dev/null
+++ b/ArcFormats/Fog/ArcDAT.cs
@@ -0,0 +1,93 @@
+//! \file       ArcDAT.cs
+//! \date       2026-01-24
+//! \brief      FOG resource archive format.
+//
+// Copyright (C) 2026 by morkt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using GameRes.Utility;
+
+namespace GameRes.Formats.Fog {
+    internal class DatEntry : Entry {
+        public string FileName;
+    }
+
+    [Export(typeof(ArchiveFormat))]
+    public class DatOpener : ArchiveFormat {
+        public override string         Tag { get { return "DAT/FOG"; } }
+        public override string Description { get { return "FOG resource archive"; } }
+        public override uint     Signature { get { return 0; } }
+        public override bool  IsHierarchic { get { return true; } }
+        public override bool      CanWrite { get { return false; } }
+
+        public override ArcFile TryOpen(ArcView file) {
+            var base_name = Path.GetFileNameWithoutExtension(file.Name);
+            bool multipart = base_name.Contains("_");
+            if (multipart)
+                base_name = base_name.Split('_')[0];
+            var index_file_name = base_name + "File.dat";
+            if (!File.Exists(index_file_name))
+                return null;
+
+            var index = File.ReadAllBytes(index_file_name);
+            var transformer = new NotTransform();
+            transformer.TransformBlock(index, 0, index.Length, index, 0);
+
+            using (var mem = new MemoryStream(index))
+            using (var reader = new BinaryReader(mem)) {
+                var dir = new List<Entry>();
+
+                while (mem.Position < mem.Length) {
+                    uint name_length = Binary.BigEndian(reader.ReadUInt32());
+                    string name = Binary.GetCString(reader.ReadBytes((int)name_length), 0);
+                    var entry = Create<DatEntry>(name);
+                    if (multipart) {
+                        uint part = Binary.BigEndian(reader.ReadUInt32());
+                        entry.FileName = string.Format("{0}_{1:00}.dat", base_name, part);
+                        if (!File.Exists(entry.FileName))
+                            return null;
+                    }
+                    else {
+                        entry.FileName = file.Name;
+                    }
+                    reader.ReadUInt32();
+                    entry.Offset = Binary.BigEndian(reader.ReadUInt32());
+                    reader.ReadUInt32();
+                    entry.Size = Binary.BigEndian(reader.ReadUInt32());
+                    dir.Add(entry);
+                }
+
+                return new ArcFile(file, this, dir);
+            }
+        }
+
+        public override Stream OpenEntry(ArcFile arc, Entry entry) {
+            var dent = entry as DatEntry;
+            using (var data_file = new ArcView(dent.FileName)) {
+                var input = data_file.CreateStream(dent.Offset, dent.Size);
+                return new XoredStream(input, 0xFF);
+            }
+        }
+    }
+}