diff --git a/src/Instrumentation/IO/README.md b/src/Instrumentation/IO/README.md
index 0ffb86b02..c63ceca6d 100644
--- a/src/Instrumentation/IO/README.md
+++ b/src/Instrumentation/IO/README.md
@@ -22,6 +22,10 @@ following functions:
 - `file_put_contents`
 - `curl_init`
 - `curl_exec`
+- `ob_start`
+- `ob_clean`
+- `ob_flush`
+- `flush`
 
 ## Configuration
 
@@ -29,4 +33,4 @@ The extension can be disabled via [runtime configuration](https://opentelemetry.
 
 ```shell
 OTEL_PHP_DISABLED_INSTRUMENTATIONS=io
-```
\ No newline at end of file
+```
diff --git a/src/Instrumentation/IO/src/IOInstrumentation.php b/src/Instrumentation/IO/src/IOInstrumentation.php
index 0582960f7..04821991e 100644
--- a/src/Instrumentation/IO/src/IOInstrumentation.php
+++ b/src/Instrumentation/IO/src/IOInstrumentation.php
@@ -33,6 +33,12 @@ public static function register(): void
         self::_hook($instrumentation, null, 'file_get_contents', 'file_get_contents');
         self::_hook($instrumentation, null, 'file_put_contents', 'file_put_contents');
 
+        // Output buffer functions
+        self::_hook($instrumentation, null, 'ob_start', 'ob_start');
+        self::_hook($instrumentation, null, 'ob_clean', 'ob_clean');
+        self::_hook($instrumentation, null, 'ob_flush', 'ob_flush');
+        self::_hook($instrumentation, null, 'flush', 'flush');
+  
         self::_hook($instrumentation, null, 'curl_init', 'curl_init');
         self::_hook($instrumentation, null, 'curl_exec', 'curl_exec');
     }
@@ -109,6 +115,19 @@ private static function addParams(SpanBuilderInterface $builder, string $functio
             case 'file_put_contents':
                 $builder->setAttribute('code.params.filename', $params[0]);
 
+                break;
+            case 'ob_start':
+                if (isset($params[0]) && is_callable($params[0])) {
+                    // We can't directly serialize the callback, so we'll just note that one was provided
+                    $builder->setAttribute('code.params.has_callback', true);
+                }
+                if (isset($params[1])) {
+                    $builder->setAttribute('code.params.chunk_size', $params[1]);
+                }
+                if (isset($params[2])) {
+                    $builder->setAttribute('code.params.flags', $params[2]);
+                }
+
                 break;
         }
     }
diff --git a/src/Instrumentation/IO/tests/Integration/IOInstrumentationTest.php b/src/Instrumentation/IO/tests/Integration/IOInstrumentationTest.php
index f9f49044e..d23564c16 100644
--- a/src/Instrumentation/IO/tests/Integration/IOInstrumentationTest.php
+++ b/src/Instrumentation/IO/tests/Integration/IOInstrumentationTest.php
@@ -37,6 +37,10 @@ public function setUp(): void
     public function tearDown(): void
     {
         $this->scope->detach();
+        // Clean up any output buffers that might have been started during tests
+        while (ob_get_level() > 0) {
+            ob_end_clean();
+        }
     }
 
     public function test_io_calls(): void
@@ -83,4 +87,44 @@ public function test_io_calls(): void
         $this->span = $this->storage->offsetGet(6);
         $this->assertSame('curl_exec', $this->span->getName());
     }
+
+    public function test_output_buffer_calls(): void
+    {
+        // Make sure we start with a clean state
+        while (ob_get_level() > 0) {
+            ob_end_clean();
+        }
+        // Test ob_start with parameters
+        $callback = function ($buffer) {
+            return $buffer;
+        };
+        ob_start($callback, 4096, PHP_OUTPUT_HANDLER_STDFLAGS);
+        $this->assertCount(1, $this->storage);
+        $this->span = $this->storage->offsetGet(0);
+        $this->assertSame('ob_start', $this->span->getName());
+        $this->assertTrue($this->span->getAttributes()->get('code.params.has_callback'));
+        $this->assertSame(4096, $this->span->getAttributes()->get('code.params.chunk_size'));
+        $this->assertSame(PHP_OUTPUT_HANDLER_STDFLAGS, $this->span->getAttributes()->get('code.params.flags'));
+        
+        // Test ob_clean
+        ob_clean();
+        $this->assertCount(2, $this->storage);
+        $this->span = $this->storage->offsetGet(1);
+        $this->assertSame('ob_clean', $this->span->getName());
+        
+        // Test ob_flush
+        ob_flush();
+        $this->assertCount(3, $this->storage);
+        $this->span = $this->storage->offsetGet(2);
+        $this->assertSame('ob_flush', $this->span->getName());
+        
+        // Test flush
+        flush();
+        $this->assertCount(4, $this->storage);
+        $this->span = $this->storage->offsetGet(3);
+        $this->assertSame('flush', $this->span->getName());
+        
+        // Clean up
+        ob_end_clean();
+    }
 }