diff --git a/RestSharp.IntegrationTests/oAuth1Tests.cs b/RestSharp.IntegrationTests/oAuth1Tests.cs
index 9387514c5..d9002c680 100644
--- a/RestSharp.IntegrationTests/oAuth1Tests.cs
+++ b/RestSharp.IntegrationTests/oAuth1Tests.cs
@@ -171,5 +171,20 @@ public void Properly_Encodes_Parameter_Names()
 
             Assert.Equal("name%5Bfirst%5D", sortedParams[0].Name);
         }
+
+		[Fact]
+		public void Use_RFC_3986_Encoding_For_Auth_Signature_Base()
+		{
+			// reserved characters for 2396 and 3986
+			var reserved2396Characters = new[] { ";", "/", "?", ":", "@", "&", "=", "+", "$", "," }; // http://www.ietf.org/rfc/rfc2396.txt
+			var additionalReserved3986Characters = new[] { "!", "*", "'", "(", ")" };  // http://www.ietf.org/rfc/rfc3986.txt
+			var reservedCharacterString = string.Join( string.Empty, reserved2396Characters.Union( additionalReserved3986Characters ) );
+			
+			// act
+			var escapedString = OAuthTools.UrlEncodeRelaxed( reservedCharacterString );
+
+			// assert
+			Assert.Equal( "%3B%2F%3F%3A%40%26%3D%2B%24%2C%21%2A%27%28%29", escapedString );
+		}
 	}
 }
diff --git a/RestSharp/Authenticators/OAuth/OAuthTools.cs b/RestSharp/Authenticators/OAuth/OAuthTools.cs
index 27e71ab61..d8c83dd36 100644
--- a/RestSharp/Authenticators/OAuth/OAuthTools.cs
+++ b/RestSharp/Authenticators/OAuth/OAuthTools.cs
@@ -83,16 +83,42 @@ public static string GetTimestamp(DateTime dateTime)
 			return timestamp.ToString();
 		}
 
+		/// <summary>
+		/// The set of characters that are unreserved in RFC 2396 but are NOT unreserved in RFC 3986.
+		/// </summary>
+		/// <seealso cref="http://stackoverflow.com/questions/846487/how-to-get-uri-escapedatastring-to-comply-with-rfc-3986" />
+		private static readonly string[] UriRfc3986CharsToEscape = new[] { "!", "*", "'", "(", ")" };
+
 		/// <summary>
 		/// URL encodes a string based on section 5.1 of the OAuth spec.
 		/// Namely, percent encoding with [RFC3986], avoiding unreserved characters,
 		/// upper-casing hexadecimal characters, and UTF-8 encoding for text value pairs.
 		/// </summary>
-		/// <param name="value"></param>
+		/// <param name="value">The value to escape.</param>
+		/// <returns>The escaped value.</returns>
+		/// <remarks>
+		/// The <see cref="Uri.EscapeDataString"/> method is <i>supposed</i> to take on
+		/// RFC 3986 behavior if certain elements are present in a .config file.  Even if this
+		/// actually worked (which in my experiments it <i>doesn't</i>), we can't rely on every
+		/// host actually having this configuration element present.
+		/// </remarks>
 		/// <seealso cref="http://oauth.net/core/1.0#encoding_parameters" />
+		/// <seealso cref="http://stackoverflow.com/questions/846487/how-to-get-uri-escapedatastring-to-comply-with-rfc-3986" />
 		public static string UrlEncodeRelaxed(string value)
 		{
-			return Uri.EscapeDataString(value);
+			// Start with RFC 2396 escaping by calling the .NET method to do the work.
+			// This MAY sometimes exhibit RFC 3986 behavior (according to the documentation).
+			// If it does, the escaping we do that follows it will be a no-op since the
+			// characters we search for to replace can't possibly exist in the string.
+			StringBuilder escaped = new StringBuilder(Uri.EscapeDataString(value));
+
+			// Upgrade the escaping to RFC 3986, if necessary.
+			for (int i = 0; i < UriRfc3986CharsToEscape.Length; i++) {
+				escaped.Replace(UriRfc3986CharsToEscape[i], Uri.HexEscape(UriRfc3986CharsToEscape[i][0]));
+			}
+
+			// Return the fully-RFC3986-escaped string.
+			return escaped.ToString();
 		}
 
 		/// <summary>