diff --git a/SabreTools.IO.Test/Extensions/BinaryWriterExtensionsTests.cs b/SabreTools.IO.Test/Extensions/BinaryWriterExtensionsTests.cs
index b3dce25..bb0bd22 100644
--- a/SabreTools.IO.Test/Extensions/BinaryWriterExtensionsTests.cs
+++ b/SabreTools.IO.Test/Extensions/BinaryWriterExtensionsTests.cs
@@ -11,16 +11,27 @@ using Xunit;
 namespace SabreTools.IO.Test.Extensions
 {
     // TODO: Add byte[], char[] tests
-    // TODO: Add decimal tests
     // TODO: Add string writing tests
     public class BinaryWriterExtensionsTests
     {
+        /// <summary>
+        /// Test pattern from 0x00-0x0F
+        /// </summary>
         private static readonly byte[] _bytes =
         [
             0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
             0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
         ];
 
+        /// <summary>
+        /// Represents the decimal value 0.0123456789
+        /// </summary>
+        private static readonly byte[] _decimalBytes =
+        [
+            0x15, 0xCD, 0x5B, 0x07, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0A, 0x00,
+        ];
+
         [Fact]
         public void WriteByteValueTest()
         {
@@ -346,6 +357,27 @@ namespace SabreTools.IO.Test.Extensions
             ValidateBytes(expected, stream.GetBuffer());
         }
 
+        [Fact]
+        public void WriteDecimalTest()
+        {
+            var stream = new MemoryStream(new byte[16], 0, 16, true, true);
+            var bw = new BinaryWriter(stream);
+            byte[] expected = _decimalBytes.Take(16).ToArray();
+            bw.Write(0.0123456789M);
+            ValidateBytes(expected, stream.GetBuffer());
+        }
+
+        [Fact]
+        public void WriteDecimalBigEndianTest()
+        {
+            var stream = new MemoryStream(new byte[16], 0, 16, true, true);
+            var bw = new BinaryWriter(stream);
+            byte[] expected = _decimalBytes.Take(16).Reverse().ToArray();
+            bool write = bw.WriteBigEndian(0.0123456789M);
+            Assert.True(write);
+            ValidateBytes(expected, stream.GetBuffer());
+        }
+
         [Fact]
         public void WriteGuidTest()
         {
diff --git a/SabreTools.IO.Test/Extensions/ByteArrayExtensionsWriteTests.cs b/SabreTools.IO.Test/Extensions/ByteArrayExtensionsWriteTests.cs
index 01004fe..f5d4512 100644
--- a/SabreTools.IO.Test/Extensions/ByteArrayExtensionsWriteTests.cs
+++ b/SabreTools.IO.Test/Extensions/ByteArrayExtensionsWriteTests.cs
@@ -8,16 +8,27 @@ using Xunit;
 
 namespace SabreTools.IO.Test.Extensions
 {
-    // TODO: Add decimal tests
     // TODO: Add string writing tests
     public class ByteArrayExtensionsWriteTests
     {
+        /// <summary>
+        /// Test pattern from 0x00-0x0F
+        /// </summary>
         private static readonly byte[] _bytes =
         [
             0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
             0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
         ];
 
+        /// <summary>
+        /// Represents the decimal value 0.0123456789
+        /// </summary>
+        private static readonly byte[] _decimalBytes =
+        [
+            0x15, 0xCD, 0x5B, 0x07, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0A, 0x00,
+        ];
+
         [Fact]
         public void WriteByteTest()
         {
@@ -328,6 +339,28 @@ namespace SabreTools.IO.Test.Extensions
             ValidateBytes(expected, buffer);
         }
 
+        [Fact]
+        public void WriteDecimalTest()
+        {
+            byte[] buffer = new byte[16];
+            int offset = 0;
+            byte[] expected = _decimalBytes.Take(16).ToArray();
+            bool write = buffer.Write(ref offset, 0.0123456789M);
+            Assert.True(write);
+            ValidateBytes(expected, buffer);
+        }
+
+        [Fact]
+        public void WriteDecimalBigEndianTest()
+        {
+            byte[] buffer = new byte[16];
+            int offset = 0;
+            byte[] expected = _decimalBytes.Take(16).Reverse().ToArray();
+            bool write = buffer.WriteBigEndian(ref offset, 0.0123456789M);
+            Assert.True(write);
+            ValidateBytes(expected, buffer);
+        }
+
         [Fact]
         public void WriteGuidTest()
         {
diff --git a/SabreTools.IO.Test/Extensions/StreamExtensionsWriteTests.cs b/SabreTools.IO.Test/Extensions/StreamExtensionsWriteTests.cs
index a8da03f..af932cf 100644
--- a/SabreTools.IO.Test/Extensions/StreamExtensionsWriteTests.cs
+++ b/SabreTools.IO.Test/Extensions/StreamExtensionsWriteTests.cs
@@ -9,16 +9,27 @@ using Xunit;
 
 namespace SabreTools.IO.Test.Extensions
 {
-    // TODO: Add decimal tests
     // TODO: Add string writing tests
     public class StreamExtensionsWriteTests
     {
+        /// <summary>
+        /// Test pattern from 0x00-0x0F
+        /// </summary>
         private static readonly byte[] _bytes =
         [
             0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
             0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
         ];
 
+        /// <summary>
+        /// Represents the decimal value 0.0123456789
+        /// </summary>
+        private static readonly byte[] _decimalBytes =
+        [
+            0x15, 0xCD, 0x5B, 0x07, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0A, 0x00,
+        ];
+
         [Fact]
         public void WriteByteValueTest()
         {
@@ -301,6 +312,26 @@ namespace SabreTools.IO.Test.Extensions
             ValidateBytes(expected, stream.GetBuffer());
         }
 
+        [Fact]
+        public void WriteDecimalTest()
+        {
+            var stream = new MemoryStream(new byte[16], 0, 16, true, true);
+            byte[] expected = _decimalBytes.Take(16).ToArray();
+            bool write = stream.Write(0.0123456789M);
+            Assert.True(write);
+            ValidateBytes(expected, stream.GetBuffer());
+        }
+
+        [Fact]
+        public void WriteDecimalBigEndianTest()
+        {
+            var stream = new MemoryStream(new byte[16], 0, 16, true, true);
+            byte[] expected = _decimalBytes.Take(16).Reverse().ToArray();
+            bool write = stream.WriteBigEndian(0.0123456789M);
+            Assert.True(write);
+            ValidateBytes(expected, stream.GetBuffer());
+        }
+
         [Fact]
         public void WriteGuidTest()
         {