diff --git a/Asn1Parser/Asn1Reader.cs b/Asn1Parser/Asn1Reader.cs
index 51207af..aa408ed 100644
--- a/Asn1Parser/Asn1Reader.cs
+++ b/Asn1Parser/Asn1Reader.cs
@@ -22,15 +22,17 @@ namespace SysadminsLV.Asn1Parser;
 /// </remarks>
 public class Asn1Reader {
     // a list of primitive tags. Source: http://en.wikipedia.org/wiki/Distinguished_Encoding_Rules#DER_encoding
-    static readonly List<Byte> _excludedTags = [ 0, 1, 2, 5, 6, 9, 10, 13 ];
+    // although we actively do lookups, it is NOT recommended to use sets (HashSet<T>), because at current collection size
+    // lookups in HashSet are around 3-4x times slower than in plain list.
+    static readonly List<Byte> _excludedTags = [ 0, 1, 2, 5, 6, 9, 10, 12, 13, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 ];
+    static readonly List<Byte> _multiNestedTypes = [
+        (Byte)Asn1Type.SEQUENCE,
+        (Byte)Asn1Type.SEQUENCE | (Byte)Asn1Class.CONSTRUCTED,
+        (Byte)Asn1Type.SET,
+        (Byte)Asn1Type.SET | (Byte)Asn1Class.CONSTRUCTED
+    ];
     readonly List<Byte> _rawData = [];
     readonly Dictionary<Int64, AsnInternalMap> _offsetMap = [];
-    readonly List<Byte> _multiNestedTypes = [
-                  (Byte)Asn1Type.SEQUENCE,
-                  (Byte)Asn1Type.SEQUENCE | (Byte)Asn1Class.CONSTRUCTED,
-                  (Byte)Asn1Type.SET,
-                  (Byte)Asn1Type.SET | (Byte)Asn1Class.CONSTRUCTED
-              ];
     AsnInternalMap currentPosition;
     Int32 childCount;
 
diff --git a/tests/Asn1Parser.Tests/CollectionPerfTests.cs b/tests/Asn1Parser.Tests/CollectionPerfTests.cs
new file mode 100644
index 0000000..d07de4b
--- /dev/null
+++ b/tests/Asn1Parser.Tests/CollectionPerfTests.cs
@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Asn1Parser.Tests;
+[TestClass]
+public class CollectionPerfTests {
+    static readonly List<Byte> _list = [0, 1, 2, 5, 6, 9, 10, 12, 13, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30];
+    static readonly HashSet<Byte> _hashSet = [0, 1, 2, 5, 6, 9, 10, 12, 13, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30];
+    const Int32 ITERATIONS = 1000000;
+
+    [TestMethod]
+    public void TestFirstMatch() {
+        assertGlobal(0);
+    }
+    [TestMethod]
+    public void TestMiddleMatch() {
+        assertGlobal(20);
+    }
+    [TestMethod]
+    public void TestLastMatch() {
+        assertGlobal(30);
+    }
+    [TestMethod]
+    public void TestNoMatch() {
+        assertGlobal(255);
+    }
+
+    static void assertGlobal(Byte searchByte) {
+        TimeSpan list = executeAction(_list.Contains, searchByte, ITERATIONS);
+        TimeSpan hashSet = executeAction(_hashSet.Contains, searchByte, ITERATIONS);
+        assertListIsFaster(list, hashSet);
+    }
+    static void assertListIsFaster(TimeSpan list, TimeSpan hashSet) {
+        Assert.IsTrue(list < hashSet);
+    }
+    //static void assertListIsFaster3xTimes(TimeSpan list, TimeSpan hashSet) {
+    //    Double ratio = hashSet / list;
+    //    Console.WriteLine(ratio);
+    //    Assert.IsTrue(ratio >= 3);
+    //}
+    static TimeSpan executeAction(Func<Byte, Boolean> action, Byte searchValue, Int32 iterations) {
+        var sw = new Stopwatch();
+        sw.Start();
+        for (Int32 i = 0; i < iterations; i++) {
+            action.Invoke(searchValue);
+        }
+        sw.Stop();
+
+        return sw.Elapsed;
+    }
+}