diff --git a/CHANGES.md b/CHANGES.md
index 75a319d..691a6da 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,6 @@
+## 0.0.9 (2023/05/16)
+* Added maximum concurrency setting
+
 ## 0.0.8 (2023/05/06)
 * CHANGED: build process
 * ADDED: GitHub actions
diff --git a/src/Benchmarks/BatchBuilder1.cs b/src/Benchmarks/BatchBuilder1.cs
new file mode 100644
index 0000000..312994e
--- /dev/null
+++ b/src/Benchmarks/BatchBuilder1.cs
@@ -0,0 +1,55 @@
+using System.Collections.Concurrent;
+using BenchmarkDotNet.Attributes;
+using K4os.Async.Toys;
+
+namespace Benchmarks;
+
+public class BatchBuilder1
+{
+	private const int Concurrency = 64;
+	private readonly SemaphoreSlim _semaphore = new(Concurrency);
+	private const int OpCount = 10000;
+	private readonly ConcurrentBag<int> _bag = new();
+
+	private readonly IBatchBuilder<int, int> _batchBuilder;
+
+	public BatchBuilder1()
+	{
+		_batchBuilder = BatchBuilder.Create<int, int, int>(
+			request => request,
+			response => response,
+			NoOpN,
+			new BatchBuilderSettings { BatchSize = 10, Concurrency = Concurrency });
+	}
+
+	[Benchmark]
+	public void Straight()
+	{
+		Task.WhenAll(Enumerable.Range(0, OpCount).Select(NoOp1)).Wait();
+	}
+	
+	[Benchmark]
+	public void AsBatch()
+	{
+		Task.WhenAll(Enumerable.Range(0, OpCount).Select(_batchBuilder.Request)).Wait();
+	}
+
+	private async Task<int[]> NoOpN(int[] requests)
+	{
+		await _semaphore.WaitAsync();
+		await Delay();
+		foreach (var request in requests) _bag.Add(request);
+		_semaphore.Release();
+		return requests;
+	}
+
+	private async Task NoOp1(int i)
+	{
+		await _semaphore.WaitAsync();
+		await Delay();
+		_bag.Add(i);
+		_semaphore.Release();
+	}
+
+	private static Task Delay() => Task.Delay(1);
+}
diff --git a/src/Benchmarks/Benchmarks.csproj b/src/Benchmarks/Benchmarks.csproj
new file mode 100644
index 0000000..d6a2644
--- /dev/null
+++ b/src/Benchmarks/Benchmarks.csproj
@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="BenchmarkDotNet" Version="0.13.5" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\K4os.Async.Toys\K4os.Async.Toys.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/Benchmarks/Program.cs b/src/Benchmarks/Program.cs
new file mode 100644
index 0000000..d11060a
--- /dev/null
+++ b/src/Benchmarks/Program.cs
@@ -0,0 +1,5 @@
+// See https://aka.ms/new-console-template for more information
+
+using BenchmarkDotNet.Running;
+
+BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);
diff --git a/src/K4os.Async.Toys.sln b/src/K4os.Async.Toys.sln
index 52b6680..f8b676b 100644
--- a/src/K4os.Async.Toys.sln
+++ b/src/K4os.Async.Toys.sln
@@ -33,6 +33,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "K4os.Async.Toys.Tests", "K4
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "K4os.Async.Toys.App", "K4os.Async.Toys.App\K4os.Async.Toys.App.csproj", "{3E541988-CA33-477D-907E-DA43944AF400}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Benchmarks", "Benchmarks\Benchmarks.csproj", "{BA1AD6AB-F72E-4A0C-ACA7-AA328C70CD59}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -53,6 +55,10 @@ Global
 		{3E541988-CA33-477D-907E-DA43944AF400}.Release|Any CPU.Build.0 = Release|Any CPU
 		{17C2C146-01F7-4C31-89FF-F20958A8C147}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{17C2C146-01F7-4C31-89FF-F20958A8C147}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BA1AD6AB-F72E-4A0C-ACA7-AA328C70CD59}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{BA1AD6AB-F72E-4A0C-ACA7-AA328C70CD59}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{BA1AD6AB-F72E-4A0C-ACA7-AA328C70CD59}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BA1AD6AB-F72E-4A0C-ACA7-AA328C70CD59}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
diff --git a/src/K4os.Async.Toys/AliveKeeper.cs b/src/K4os.Async.Toys/AliveKeeper.cs
index 19db261..67bb158 100644
--- a/src/K4os.Async.Toys/AliveKeeper.cs
+++ b/src/K4os.Async.Toys/AliveKeeper.cs
@@ -96,7 +96,7 @@ public AliveKeeper(
 			new BatchBuilderSettings {
 				BatchSize = settings.TouchBatchSize,
 				BatchDelay = settings.TouchBatchDelay,
-				Concurrency = 1,
+				Concurrency = settings.Concurrency,
 			},
 			log, time);
 
@@ -105,7 +105,7 @@ public AliveKeeper(
 			new BatchBuilderSettings {
 				BatchSize = settings.DeleteBatchSize,
 				BatchDelay = TimeSpan.Zero,
-				Concurrency = 1,
+				Concurrency = settings.Concurrency,
 			},
 			log, time);
 	}
@@ -118,6 +118,7 @@ private static IAliveKeeperSettings Validate(IAliveKeeperSettings settings) =>
 			DeleteBatchSize = settings.DeleteBatchSize.NotLessThan(1),
 			RetryInterval = settings.RetryInterval.NotLessThan(TimeSpan.Zero),
 			RetryLimit = settings.RetryLimit.NotLessThan(0),
+			Concurrency = settings.Concurrency.NotLessThan(1),
 		};
 
 	private static T Pass(T x) => x;
@@ -217,6 +218,7 @@ private async Task DeleteOne(string display, T item)
 	/// <param name="key">Key.</param>
 	/// <returns>Key in human readable format.</returns>
 	protected virtual string Display(T key) =>
+		// ReSharper disable once NullCoalescingConditionIsAlwaysNotNullAccordingToAPIContract
 		_keyToString?.Invoke(key) ?? key.ToString() ?? "<null>";
 
 	private async Task TouchOneLoop(T item, CancellationToken token)
diff --git a/src/K4os.Async.Toys/AliveKeeperSettings.cs b/src/K4os.Async.Toys/AliveKeeperSettings.cs
index 05caafb..cfaf789 100644
--- a/src/K4os.Async.Toys/AliveKeeperSettings.cs
+++ b/src/K4os.Async.Toys/AliveKeeperSettings.cs
@@ -26,6 +26,9 @@ public interface IAliveKeeperSettings
 
 	/// <summary>Number of retries for deletion.</summary>
 	int RetryLimit { get; }
+
+	/// <summary>Level of concurrency for operations.</summary>
+	int Concurrency { get; }
 }
 
 /// <summary>
@@ -50,4 +53,7 @@ public class AliveKeeperSettings: IAliveKeeperSettings
 
 	/// <inheritdoc />
 	public int RetryLimit { get; set; }
+
+	/// <inheritdoc />
+	public int Concurrency { get; set; } = 1;
 }
\ No newline at end of file