diff --git a/src/Hl7.Fhir.Base/Rest/BaseFhirClient.cs b/src/Hl7.Fhir.Base/Rest/BaseFhirClient.cs
index d072424c3c..0a62a8cc18 100644
--- a/src/Hl7.Fhir.Base/Rest/BaseFhirClient.cs
+++ b/src/Hl7.Fhir.Base/Rest/BaseFhirClient.cs
@@ -29,6 +29,7 @@ public partial class BaseFhirClient : IDisposable
     {
         internal readonly ModelInspector Inspector;
         private readonly IFhirSerializationEngine _serializationEngine;
+        private readonly Lazy<List<HttpStatusCode>> _200responses = new(() => Enum.GetValues(typeof(HttpStatusCode)).Cast<HttpStatusCode>().Where(n => (int)n > 199 && (int)n < 300).ToList());
 
         /// <summary>
         /// Creates a new client using a default endpoint
@@ -914,7 +915,8 @@ public virtual void Delete(string resourceType, SearchParams condition)
 
             var tx = new TransactionBuilder(Endpoint).EndpointOperation(new RestUrl(location), operationName, parameters, useGet).ToBundle();
 
-            return executeAsync<Resource>(tx, HttpStatusCode.OK, ct);
+            //operation responses are expected to return 2xx codes.
+            return executeAsync<Resource>(tx, _200responses.Value, ct);
         }
 
         [Obsolete("Synchronous use of the FhirClient is strongly discouraged, use the asynchronous call instead.")]
@@ -929,7 +931,8 @@ public virtual void Delete(string resourceType, SearchParams condition)
 
             var tx = new TransactionBuilder(Endpoint).EndpointOperation(new RestUrl(operation), parameters, useGet).ToBundle();
 
-            return executeAsync<Resource>(tx, HttpStatusCode.OK, ct);
+            //operation responses are expected to return 2xx codes.
+            return executeAsync<Resource>(tx, _200responses.Value, ct);
         }
 
         [Obsolete("Synchronous use of the FhirClient is strongly discouraged, use the asynchronous call instead.")]
@@ -944,7 +947,7 @@ public virtual void Delete(string resourceType, SearchParams condition)
 
             var tx = new TransactionBuilder(Endpoint).ProcessMessage(bundle, async, responseUrl).ToBundle();
 
-            return executeAsync<Bundle>(tx, new [] {HttpStatusCode.OK, HttpStatusCode.Accepted, HttpStatusCode.NoContent}, ct);
+            return executeAsync<Bundle>(tx, new[] { HttpStatusCode.OK, HttpStatusCode.Accepted, HttpStatusCode.NoContent }, ct);
         }
 
         [Obsolete("Synchronous use of the FhirClient is strongly discouraged, use the asynchronous call instead.")]
@@ -973,7 +976,8 @@ public virtual void Delete(string resourceType, SearchParams condition)
             else
                 tx = new TransactionBuilder(Endpoint).ResourceOperation(type, id, vid, operationName, parameters, useGet).ToBundle();
 
-            return executeAsync<Resource>(tx, new[] { HttpStatusCode.OK, HttpStatusCode.Accepted }, ct);
+            //operation responses are expected to return 2xx codes.
+            return executeAsync<Resource>(tx, _200responses.Value, ct);
         }
 
         private Resource? internalOperation(string operationName, string? type = null, string? id = null,
diff --git a/src/Hl7.Fhir.Support.Poco.Tests/Rest/FhirClientMockTests.cs b/src/Hl7.Fhir.Support.Poco.Tests/Rest/FhirClientMockTests.cs
index 945d77833d..abe3ca6d62 100644
--- a/src/Hl7.Fhir.Support.Poco.Tests/Rest/FhirClientMockTests.cs
+++ b/src/Hl7.Fhir.Support.Poco.Tests/Rest/FhirClientMockTests.cs
@@ -5,7 +5,6 @@
 using Hl7.Fhir.Introspection;
 using Hl7.Fhir.Model;
 using Hl7.Fhir.Rest;
-using Hl7.Fhir.Serialization;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
 using Moq.Protected;
@@ -147,7 +146,7 @@ public async T.Task AcceptHeaderTest(bool useFhirVersionHeader)
             };
 
             using var client = new MoqBuilder()
-                .Send(response, 
+                .Send(response,
                     h => h.RequestUri == new Uri("http://example.com/Patient?name=henry") &&
                         findInAcceptHeader(h.Headers.Accept, "fhirVersion", useFhirVersionHeader))
                 .AsClient(s => { s.VerifyFhirVersion = false; s.UseFhirVersionInAcceptHeader = useFhirVersionHeader; });
@@ -347,6 +346,55 @@ public async Task WillReturnOperationOutcomeOnOtherEndpoint()
             client.LastResult!.Outcome.Should().BeOfType<OperationOutcome>().Which.Id.Should().Be("example");
         }
 
+
+        [TestMethod]
+        public async T.Task TestOperationResponseCodes()
+        {
+            var response = new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.Created,
+                Content = new StringContent(@"{""resourceType"": ""Parameters"",  ""parameter"": [ { ""name"": ""result"", ""valueString"": ""connected""}]  }", Encoding.UTF8, "application/json"),
+                RequestMessage = new HttpRequestMessage(HttpMethod.Post, "http://example.com/fhir/$ping")
+            };
+
+            using var client = new MoqBuilder()
+                .Send(response, h => h.RequestUri == new Uri("http://example.com/fhir/$ping"))
+                .AsClient();
+
+            var parameters = await client.OperationAsync(new Uri("http://example.com/fhir/$ping")) as Parameters;
+            client.LastResult?.Status.Should().Be("201");
+
+            response = new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.Accepted,
+                Content = new StringContent(@"{""resourceType"": ""Parameters"",  ""parameter"": [ { ""name"": ""result"", ""valueString"": ""connected""}]  }", Encoding.UTF8, "application/json"),
+                RequestMessage = new HttpRequestMessage(HttpMethod.Post, "http://example.com/fhir/$ping")
+            };
+
+            using var client2 = new MoqBuilder()
+                .Send(response, h => h.RequestUri == new Uri("http://example.com/fhir/$ping"))
+                .AsClient();
+
+            parameters = await client2.OperationAsync(new Uri("http://example.com/fhir/$ping")) as Parameters;
+            client2.LastResult?.Status.Should().Be("202");
+
+
+            response = new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.NotFound,
+                Content = new StringContent(@"{""resourceType"": ""Parameters"",  ""parameter"": [ { ""name"": ""result"", ""valueString"": ""connected""}]  }", Encoding.UTF8, "application/json"),
+                RequestMessage = new HttpRequestMessage(HttpMethod.Post, "http://example.com/fhir/$ping")
+            };
+
+            using var client3 = new MoqBuilder()
+                .Send(response, h => h.RequestUri == new Uri("http://example.com/fhir/$ping"))
+                .AsClient();
+
+            var function = () => client3.OperationAsync(new Uri("http://example.com/fhir/$ping"));
+            await function.Should().ThrowAsync<FhirOperationException>().WithMessage("Operation was unsuccessful because of a client error (NotFound). Body contains a Parameters.");
+
+        }
+
         private static BaseFhirClient sendBack(string resourceType)
         {
             var mock = new Mock<HttpMessageHandler>();