diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index 49b51827..19d0cb70 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -177,6 +177,7 @@
     <Compile Include="FlyingShine\ArcPD.cs" />
     <Compile Include="TopCat\ArcTCD3.cs" />
     <Compile Include="TopCat\ImageSPD.cs" />
+    <Compile Include="uGOS\ArcDET.cs" />
     <Compile Include="UMeSoft\ArcPK.cs" />
     <Compile Include="Qlie\ArcQLIE.cs" />
     <Compile Include="RenPy\ArcRPA.cs" />
diff --git a/ArcFormats/uGOS/ArcDET.cs b/ArcFormats/uGOS/ArcDET.cs
new file mode 100644
index 00000000..4492028b
--- /dev/null
+++ b/ArcFormats/uGOS/ArcDET.cs
@@ -0,0 +1,130 @@
+//! \file       ArcDET.cs
+//! \date       Mon Nov 09 00:16:53 2015
+//! \brief      μ-GameOperationSystem resource archive.
+//
+// Copyright (C) 2015 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;
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using GameRes.Utility;
+
+namespace GameRes.Formats.uGOS
+{
+    [Export(typeof(ArchiveFormat))]
+    public class PakOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "DET"; } }
+        public override string Description { get { return "μ-GameOperationSystem resource archive"; } }
+        public override uint     Signature { get { return 0; } }
+        public override bool  IsHierarchic { get { return false; } }
+        public override bool     CanCreate { get { return false; } }
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            if (!file.Name.EndsWith (".det", StringComparison.InvariantCultureIgnoreCase))
+                return null;
+            var name_file = Path.ChangeExtension (file.Name, "nme");
+            var index_file = Path.ChangeExtension (file.Name, "atm");
+            if (!VFS.FileExists (name_file) || !VFS.FileExists (index_file))
+                return null;
+            using (var nme = VFS.OpenView (name_file))
+            using (var idx = VFS.OpenView (index_file))
+            {
+                var name_table = new byte[nme.MaxOffset];
+                nme.View.Read (0, name_table, 0, (uint)name_table.Length);
+                uint idx_offset = 0;
+                int count = (int)(idx.MaxOffset / 0x14);
+                if (!IsSaneCount (count))
+                    return null;
+                var dir = new List<Entry> (count);
+                for (int i = 0; i < count; ++i)
+                {
+                    int name_offset = idx.View.ReadInt32 (idx_offset);
+                    if (name_offset < 0 || name_offset >= name_table.Length)
+                        return null;
+                    var name = Binary.GetCString (name_table, name_offset, name_table.Length - name_offset);
+                    var entry = FormatCatalog.Instance.Create<PackedEntry> (name);
+                    entry.Offset = idx.View.ReadUInt32 (idx_offset + 4);
+                    entry.Size = idx.View.ReadUInt32 (idx_offset + 8);
+                    if (!entry.CheckPlacement (file.MaxOffset))
+                        return null;
+                    entry.UnpackedSize = idx.View.ReadUInt32 (idx_offset + 0x10);
+                    entry.IsPacked = true;
+                    dir.Add (entry);
+                    idx_offset += 0x14;
+                }
+                return new ArcFile (file, this, dir);
+            }
+        }
+
+        public override Stream OpenEntry (ArcFile arc, Entry entry)
+        {
+            var pent = entry as PackedEntry;
+            if (null == pent || !pent.IsPacked)
+                return base.OpenEntry (arc, entry);
+
+            var output = new byte[pent.UnpackedSize];
+            using (var input = arc.File.CreateStream (entry.Offset, entry.Size))
+            {
+                if (Unpack (input, output))
+                    return new MemoryStream (output);
+                else
+                    return base.OpenEntry (arc, entry);
+            }
+        }
+
+        bool Unpack (Stream input, byte[] output)
+        {
+            int dst = 0;
+            while (dst < output.Length)
+            {
+                int ctl = input.ReadByte();
+                if (-1 == ctl)
+                    return false;
+                if (0xFF != ctl)
+                {
+                    output[dst++] = (byte)ctl;
+                }
+                else
+                {
+                    ctl = input.ReadByte();
+                    if (-1 == ctl)
+                        return false;
+                    if (0xFF == ctl)
+                    {
+                        output[dst++] = 0xFF;
+                    }
+                    else
+                    {
+                        int offset = (ctl >> 2) + 1;
+                        int count = (ctl & 3) + 3;
+                        Binary.CopyOverlapped (output, dst-offset, dst, count);
+                        dst += count;
+                    }
+                }
+            }
+            return true;
+        }
+    }
+}