diff --git a/lib/openai/internal/logging.rb b/lib/openai/internal/logging.rb
index c671269a..c62889d5 100644
--- a/lib/openai/internal/logging.rb
+++ b/lib/openai/internal/logging.rb
@@ -21,7 +21,7 @@ module Logging
       OPAQUE_STRING_BYTES = 1_024
       SENSITIVE_BODY_KEY = /(?:api[-_]?key|authorization|credential|password|secret|signature|token)/i
       SENSITIVE_QUERY_KEY =
-        /(?:\A|[-_])(?:api[-_]?key|authorization|credential|key|password|secret|sig|signature|token)\z/i
+        /(?:(?:\A|[-_\[])(?:key|sig)|(?-i:K)ey|api[-_]?key|authorization|credentials?|password|secret|signature|token)(?:\[|\]|\z)/i
       URL_HEADER_KEY = /(?:\A|[-_])(?:location|url|uri)\z|\A(?:link|refresh)\z/i
 
       class Context
@@ -357,11 +357,13 @@ def format_observed_body(body, headers:, complete:, total_bytes:)
             return JSON.generate(scrub_value(parsed))
           end
 
-          text = body.byteslice(0, MAX_BODY_BYTES).to_s
-          text = text.encode(Encoding::UTF_8, invalid: :replace, undef: :replace)
-          return text.inspect if total_bytes <= MAX_BODY_BYTES
+          unless content_type.match?(%r{\Aapplication/x-www-form-urlencoded(?:;|\z)}i)
+            return "[TEXT BODY OMITTED] bytes=#{total_bytes}"
+          end
+          return "[FORM BODY OMITTED] bytes=#{total_bytes} reason=too_large" if total_bytes > MAX_BODY_BYTES
 
-          "#{text.inspect} [TRUNCATED bytes=#{total_bytes}]"
+          sanitized = sanitized_query(body)
+          sanitized.nil? ? "[INVALID FORM BODY OMITTED] bytes=#{total_bytes}" : sanitized.inspect
         rescue JSON::ParserError
           "[INVALID JSON BODY OMITTED] bytes=#{total_bytes}"
         end
diff --git a/test/openai/logging_security_test.rb b/test/openai/logging_security_test.rb
new file mode 100644
index 00000000..88bad35d
--- /dev/null
+++ b/test/openai/logging_security_test.rb
@@ -0,0 +1,202 @@
+# frozen_string_literal: true
+
+require "minitest/mock"
+require_relative "test_helper"
+
+class LoggingSecurityTest < Minitest::Test
+  def test_info_and_debug_logs_redact_camel_case_and_nested_query_credentials
+    credentials = {
+      "accessToken" => "camel-access-secret",
+      "accessKey" => "camel-access-key-secret",
+      "clientSecret" => "camel-client-secret",
+      "sessionToken" => "camel-session-secret",
+      "bearerToken" => "camel-bearer-secret",
+      "access_token[]" => "array-access-secret",
+      "clientSecret[]" => "array-client-secret",
+      "credentials[accessToken]" => "nested-access-secret",
+      "credentials[client_secret]" => "nested-client-secret",
+      "credentials[access_token][]" => "nested-array-secret",
+      "credentials[value]" => "nested-credential-secret"
+    }
+
+    [:info, :debug].each do |level|
+      output, request = logged_request(
+        log_level: level,
+        query: {**credentials, "safe" => "visible", "monkey" => "still-visible"}
+      )
+
+      assert_includes(output, "request complete")
+      assert_includes(output, "safe=visible")
+      assert_includes(output, "monkey=still-visible")
+      assert_includes(output, "%5BREDACTED%5D")
+
+      credentials.each_value do |secret|
+        assert_includes(request.url.to_s, secret)
+        refute_includes(output, secret)
+      end
+
+      assert_equal(level == :debug, output.include?("request started"))
+    end
+  end
+
+  def test_url_sanitization_redacts_percent_encoded_and_nested_credential_keys
+    url = URI(
+      "https://user:password@example.com/probe?" \
+      "access%54oken=encoded-access-secret&" \
+      "access%4Bey=encoded-access-key-secret&" \
+      "credentials%5Bclient%53ecret%5D=encoded-client-secret&" \
+      "access_token%5B%5D=encoded-array-secret&" \
+      "credentials%5Bvalue%5D=encoded-credential-secret&" \
+      "safe=visible"
+    )
+
+    [OpenAI::Internal::Logging.safe_url(url), OpenAI::Internal::Logging.safe_path(url)].each do |formatted|
+      assert_includes(formatted, "safe=visible")
+      assert_includes(formatted, "%5BREDACTED%5D")
+      refute_includes(formatted, "encoded-access-secret")
+      refute_includes(formatted, "encoded-access-key-secret")
+      refute_includes(formatted, "encoded-client-secret")
+      refute_includes(formatted, "encoded-array-secret")
+      refute_includes(formatted, "encoded-credential-secret")
+      refute_includes(formatted, "user:password@")
+    end
+  end
+
+  def test_debug_logs_structurally_redact_form_urlencoded_request_bodies
+    body =
+      "client_secret=client-form-secret&access_token=access-form-secret&" \
+      "accessKey=access-key-form-secret&credentials%5Bvalue%5D=credential-form-secret&" \
+      "access_token%5B%5D=array-form-secret&" \
+      "credentials%5BsessionToken%5D=nested-form-secret&" \
+      "safe=hello+world&repeat=one&repeat=two"
+    output, request = logged_request(
+      log_level: :debug,
+      headers: {"content-type" => "application/x-www-form-urlencoded; charset=utf-8"},
+      body: body
+    )
+
+    assert_equal(body, request.body)
+    assert_includes(output, "request started")
+    assert_includes(output, "client_secret=%5BREDACTED%5D")
+    assert_includes(output, "access_token=%5BREDACTED%5D")
+    assert_includes(output, "accessKey=%5BREDACTED%5D")
+    assert_includes(output, "credentials%5Bvalue%5D=%5BREDACTED%5D")
+    assert_includes(output, "access_token%5B%5D=%5BREDACTED%5D")
+    assert_includes(output, "credentials%5BsessionToken%5D=%5BREDACTED%5D")
+    assert_includes(output, "safe=hello+world")
+    assert_includes(output, "repeat=one&repeat=two")
+    refute_includes(output, "client-form-secret")
+    refute_includes(output, "access-form-secret")
+    refute_includes(output, "access-key-form-secret")
+    refute_includes(output, "credential-form-secret")
+    refute_includes(output, "array-form-secret")
+    refute_includes(output, "nested-form-secret")
+  end
+
+  def test_debug_logs_structurally_redact_form_urlencoded_response_bodies
+    body =
+      "accessToken=response-access-secret&access_token%5B%5D=response-array-secret&" \
+      "accessKey=response-access-key-secret&credentials%5Bvalue%5D=response-credential-secret&" \
+      "credentials%5Bclient_secret%5D=response-client-secret&safe=visible"
+    formatted = OpenAI::Internal::Logging.format_observed_body(
+      body,
+      headers: {"content-type" => "application/x-www-form-urlencoded"},
+      complete: true,
+      total_bytes: body.bytesize
+    )
+
+    assert_includes(formatted, "accessToken=%5BREDACTED%5D")
+    assert_includes(formatted, "accessKey=%5BREDACTED%5D")
+    assert_includes(formatted, "credentials%5Bvalue%5D=%5BREDACTED%5D")
+    assert_includes(formatted, "access_token%5B%5D=%5BREDACTED%5D")
+    assert_includes(formatted, "credentials%5Bclient_secret%5D=%5BREDACTED%5D")
+    assert_includes(formatted, "safe=visible")
+    refute_includes(formatted, "response-access-secret")
+    refute_includes(formatted, "response-access-key-secret")
+    refute_includes(formatted, "response-credential-secret")
+    refute_includes(formatted, "response-array-secret")
+    refute_includes(formatted, "response-client-secret")
+  end
+
+  def test_debug_logs_omit_malformed_or_oversized_form_bodies
+    headers = {"content-type" => "application/x-www-form-urlencoded"}
+    malformed = "access_token=malformed-secret&invalid=\xFF".b
+    oversized = "access_token=oversized-secret&padding=#{'x' * OpenAI::Internal::Logging::MAX_BODY_BYTES}"
+
+    [malformed, oversized].each do |body|
+      formatted = OpenAI::Internal::Logging.format_body(body, headers: headers)
+
+      assert_includes(formatted, "BODY OMITTED]")
+      assert_includes(formatted, "bytes=#{body.bytesize}")
+      refute_includes(formatted, "malformed-secret")
+      refute_includes(formatted, "oversized-secret")
+    end
+  end
+
+  def test_debug_logs_omit_unsupported_textual_request_and_response_bodies
+    content_types = [
+      "application/xml",
+      "application/vnd.example+xml; charset=utf-8",
+      "text/xml",
+      "text/plain",
+      "text/html",
+      "text/csv",
+      ""
+    ]
+
+    content_types.each do |content_type|
+      body = "<access_token>unsupported-text-secret</access_token>"
+      headers = {"content-type" => content_type}
+      request_body = OpenAI::Internal::Logging.format_body(body, headers: headers)
+      response_body = OpenAI::Internal::Logging.format_observed_body(
+        body,
+        headers: headers,
+        complete: true,
+        total_bytes: body.bytesize
+      )
+
+      [request_body, response_body].each do |formatted|
+        assert_includes(formatted, "BODY OMITTED]")
+        assert_includes(formatted, "bytes=#{body.bytesize}")
+        refute_includes(formatted, "unsupported-text-secret")
+      end
+    end
+  end
+
+  private def logged_request(log_level:, query: nil, headers: nil, body: nil)
+    output = StringIO.new
+    logger = Logger.new(output)
+    response = OpenAI::HTTPClient::Response.new(
+      status: 200,
+      headers: {"content-type" => "application/json", "x-request-id" => "req_security"},
+      body: '{"ok":true}'
+    )
+    request = nil
+    transport = Minitest::Mock.new(Object.new)
+    transport.expect(:execute, response) do |value|
+      request = value
+      value.is_a?(OpenAI::HTTPClient::Request)
+    end
+    client = OpenAI::Client.new(
+      api_key: "test-key",
+      base_url: "https://example.com/v1",
+      http_client: transport,
+      logger: logger,
+      log_level: log_level
+    )
+
+    assert_equal(
+      true,
+      client.request(
+        method: body.nil? ? :get : :post,
+        path: "probe",
+        query: query,
+        headers: headers,
+        body: body
+      )[:ok]
+    )
+    assert_mock(transport)
+
+    [output.string, request]
+  end
+end