diff --git a/composer.json b/composer.json
index 775763f58..c53bbebff 100644
--- a/composer.json
+++ b/composer.json
@@ -120,7 +120,8 @@
     "autoload-dev": {
         "psr-4": {
             "PhpOffice\\PhpSpreadsheetTests\\": "tests/PhpSpreadsheetTests",
-            "PhpOffice\\PhpSpreadsheetInfra\\": "infra"
+            "PhpOffice\\PhpSpreadsheetInfra\\": "infra",
+            "PhpOffice\\PhpSpreadsheetBenchmarks\\": "tests/Benchmark"
         }
     }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index d3e845c1e..5c9ef847d 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,13 +1,18 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.1/phpunit.xsd" bootstrap="./tests/bootstrap.php" backupGlobals="true" colors="true" cacheResultFile="/tmp/.phpspreadsheet.phpunit.result.cache">
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.1/phpunit.xsd" bootstrap="./tests/bootstrap.php" backupGlobals="true" colors="true" cacheResultFile="/tmp/.phpspreadsheet.phpunit.result.cache" defaultTestSuite="PhpSpreadsheet Unit Test Suite">
   <coverage/>
   <php>
     <ini name="memory_limit" value="2048M"/>
     <ini name="error_reporting" value="E_ALL"/>
   </php>
-  <testsuite name="PhpSpreadsheet Unit Test Suite">
-    <directory>./tests/PhpSpreadsheetTests</directory>
-  </testsuite>
+  <testsuites>
+    <testsuite name="PhpSpreadsheet Unit Test Suite">
+      <directory>./tests/PhpSpreadsheetTests</directory>
+    </testsuite>
+    <testsuite name="Benchmark">
+      <directory>./tests/Benchmark</directory>
+    </testsuite>
+  </testsuites>
   <source>
     <include>
       <directory suffix=".php">./src</directory>
diff --git a/tests/Benchmark/XlsReaderBenchmarkTest.php b/tests/Benchmark/XlsReaderBenchmarkTest.php
new file mode 100644
index 000000000..f03f90e60
--- /dev/null
+++ b/tests/Benchmark/XlsReaderBenchmarkTest.php
@@ -0,0 +1,310 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetBenchmarks;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xls as XlsReader;
+use PhpOffice\PhpSpreadsheet\Shared\File;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Style\Border;
+use PhpOffice\PhpSpreadsheet\Style\Color;
+use PhpOffice\PhpSpreadsheet\Style\Fill;
+use PhpOffice\PhpSpreadsheet\Writer\Xls as XlsWriter;
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Benchmarks for the XLS (BIFF8) reader.
+ *
+ * Run with: vendor/bin/phpunit --testsuite Benchmark --filter XlsReaderBenchmarkTest --stderr
+ */
+#[Group('benchmark')]
+class XlsReaderBenchmarkTest extends TestCase
+{
+    private const XLS_FIXTURES_DIR = 'tests/data/Reader/XLS';
+
+    /** @var string[] */
+    private array $tempFiles = [];
+
+    protected function tearDown(): void
+    {
+        foreach ($this->tempFiles as $file) {
+            if (file_exists($file)) {
+                unlink($file);
+            }
+        }
+        $this->tempFiles = [];
+    }
+
+    /**
+     * Benchmark reading a set of real XLS test fixtures.
+     *
+     * Exercises the full reader path: SST parsing, cell reads with styles,
+     * formulas, rich text, conditional formatting, and data validation.
+     */
+    public function testRealXlsFixtures(): void
+    {
+        $fixtures = [
+            self::XLS_FIXTURES_DIR . '/biff8cover.xls',
+            self::XLS_FIXTURES_DIR . '/formulas.xls',
+            self::XLS_FIXTURES_DIR . '/RichTextFontSize.xls',
+            self::XLS_FIXTURES_DIR . '/Colours.xls',
+            self::XLS_FIXTURES_DIR . '/PageSetup.xls',
+            self::XLS_FIXTURES_DIR . '/DataValidation.xls',
+        ];
+
+        foreach ($fixtures as $fixture) {
+            self::assertFileExists($fixture, "Fixture missing: {$fixture}");
+        }
+
+        $iterations = 5;
+        $reader = new XlsReader();
+
+        // Warm up
+        $warmup = $reader->load($fixtures[0]);
+        $warmup->disconnectWorksheets();
+        unset($warmup);
+
+        gc_collect_cycles();
+        $memBefore = memory_get_usage(true);
+        $start = hrtime(true);
+
+        for ($iter = 0; $iter < $iterations; ++$iter) {
+            foreach ($fixtures as $fixture) {
+                $spreadsheet = $reader->load($fixture);
+                $spreadsheet->disconnectWorksheets();
+                unset($spreadsheet);
+            }
+        }
+
+        $end = hrtime(true);
+        $memAfter = memory_get_usage(true);
+        gc_collect_cycles();
+
+        $totalMs = ($end - $start) / 1_000_000;
+        $avgMs = $totalMs / $iterations;
+        $memDeltaMb = ($memAfter - $memBefore) / 1024 / 1024;
+
+        fwrite(STDERR, "\n");
+        fwrite(STDERR, sprintf("=== XLS Real Fixtures Benchmark (%d files, %d iterations) ===\n", count($fixtures), $iterations));
+        fwrite(STDERR, sprintf("  PHP version:   %s (%s)\n", PHP_VERSION, PHP_OS));
+        fwrite(STDERR, sprintf("  Total:         %.2f ms (%.2f ms avg per iteration)\n", $totalMs, $avgMs));
+        fwrite(STDERR, sprintf("  Per file avg:  %.2f ms\n", $avgMs / count($fixtures)));
+        fwrite(STDERR, sprintf("  Memory delta:  %.2f MB\n", $memDeltaMb));
+        fwrite(STDERR, "\n");
+
+        // Verify the reader still produces valid output
+        $spreadsheet = $reader->load($fixtures[0]);
+        self::assertGreaterThan(0, $spreadsheet->getSheetCount());
+        $spreadsheet->disconnectWorksheets();
+    }
+
+    /**
+     * Benchmark reading a synthetic XLS file with many cells.
+     *
+     * Targets per-cell overhead: setXfIndexNoUpdate(), cached read filter,
+     * pre-computed cell coordinates.
+     */
+    public function testSyntheticManyCells(): void
+    {
+        $xlsFile = $this->createSyntheticXls(
+            sheets: 3,
+            rowsPerSheet: 500,
+            columnsPerSheet: 8,
+            withStyles: true,
+            withFormulas: true
+        );
+
+        $iterations = 5;
+        $reader = new XlsReader();
+
+        // Warm up
+        $warmup = $reader->load($xlsFile);
+        $totalCells = 0;
+        foreach ($warmup->getWorksheetIterator() as $sheet) {
+            $totalCells += count($sheet->getCellCollection()->getCoordinates());
+        }
+        $warmup->disconnectWorksheets();
+        unset($warmup);
+
+        gc_collect_cycles();
+        $memBefore = memory_get_usage(true);
+        $start = hrtime(true);
+
+        for ($iter = 0; $iter < $iterations; ++$iter) {
+            $spreadsheet = $reader->load($xlsFile);
+            $spreadsheet->disconnectWorksheets();
+            unset($spreadsheet);
+        }
+
+        $end = hrtime(true);
+        $memAfter = memory_get_usage(true);
+        gc_collect_cycles();
+
+        $totalMs = ($end - $start) / 1_000_000;
+        $avgMs = $totalMs / $iterations;
+        $memDeltaMb = ($memAfter - $memBefore) / 1024 / 1024;
+
+        fwrite(STDERR, "\n");
+        fwrite(STDERR, sprintf("=== XLS Synthetic Many-Cell Benchmark (%d cells, %d iterations) ===\n", $totalCells, $iterations));
+        fwrite(STDERR, sprintf("  PHP version:   %s (%s)\n", PHP_VERSION, PHP_OS));
+        fwrite(STDERR, sprintf("  Total:         %.2f ms (%.2f ms avg per iteration)\n", $totalMs, $avgMs));
+        fwrite(STDERR, sprintf("  Memory delta:  %.2f MB\n", $memDeltaMb));
+        fwrite(STDERR, "\n");
+
+        // Verify correctness
+        $spreadsheet = $reader->load($xlsFile);
+        self::assertSame(3, $spreadsheet->getSheetCount());
+        $firstSheet = $spreadsheet->getSheet(0);
+        self::assertNotNull($firstSheet->getCell('A1')->getValue());
+        $spreadsheet->disconnectWorksheets();
+    }
+
+    /**
+     * Benchmark reading a synthetic XLS file heavy on shared strings (SST).
+     *
+     * Targets SST parsing: chunk_split optimization for compressed-to-uncompressed
+     * expansion and CONTINUE record handling.
+     */
+    public function testSyntheticSstHeavy(): void
+    {
+        $xlsFile = $this->createSstHeavyXls(rows: 1000, columns: 10);
+
+        $iterations = 5;
+        $reader = new XlsReader();
+
+        // Warm up
+        $warmup = $reader->load($xlsFile);
+        $totalCells = 0;
+        foreach ($warmup->getWorksheetIterator() as $sheet) {
+            $totalCells += count($sheet->getCellCollection()->getCoordinates());
+        }
+        $warmup->disconnectWorksheets();
+        unset($warmup);
+
+        gc_collect_cycles();
+        $memBefore = memory_get_usage(true);
+        $start = hrtime(true);
+
+        for ($iter = 0; $iter < $iterations; ++$iter) {
+            $spreadsheet = $reader->load($xlsFile);
+            $spreadsheet->disconnectWorksheets();
+            unset($spreadsheet);
+        }
+
+        $end = hrtime(true);
+        $memAfter = memory_get_usage(true);
+        gc_collect_cycles();
+
+        $totalMs = ($end - $start) / 1_000_000;
+        $avgMs = $totalMs / $iterations;
+        $memDeltaMb = ($memAfter - $memBefore) / 1024 / 1024;
+
+        fwrite(STDERR, "\n");
+        fwrite(STDERR, sprintf("=== XLS SST-Heavy Benchmark (%d string cells, %d iterations) ===\n", $totalCells, $iterations));
+        fwrite(STDERR, sprintf("  PHP version:   %s (%s)\n", PHP_VERSION, PHP_OS));
+        fwrite(STDERR, sprintf("  Total:         %.2f ms (%.2f ms avg per iteration)\n", $totalMs, $avgMs));
+        fwrite(STDERR, sprintf("  Memory delta:  %.2f MB\n", $memDeltaMb));
+        fwrite(STDERR, "\n");
+
+        // Verify correctness
+        $spreadsheet = $reader->load($xlsFile);
+        $sheet = $spreadsheet->getActiveSheet();
+        self::assertIsString($sheet->getCell('A1')->getValue());
+        self::assertGreaterThan(0, strlen((string) $sheet->getCell('A1')->getValue()));
+        $spreadsheet->disconnectWorksheets();
+    }
+
+    /**
+     * Create a synthetic XLS file with mixed data, styles, and formulas.
+     */
+    private function createSyntheticXls(
+        int $sheets,
+        int $rowsPerSheet,
+        int $columnsPerSheet,
+        bool $withStyles,
+        bool $withFormulas,
+    ): string {
+        $spreadsheet = new Spreadsheet();
+        $columns = array_map(
+            fn (int $i) => \PhpOffice\PhpSpreadsheet\Cell\Coordinate::stringFromColumnIndex($i),
+            range(1, $columnsPerSheet)
+        );
+
+        for ($s = 0; $s < $sheets; ++$s) {
+            $sheet = ($s === 0) ? $spreadsheet->getActiveSheet() : $spreadsheet->createSheet();
+            $sheet->setTitle("Sheet{$s}");
+
+            for ($row = 1; $row <= $rowsPerSheet; ++$row) {
+                foreach ($columns as $colIdx => $col) {
+                    if ($withFormulas && $colIdx === $columnsPerSheet - 1 && $row > 1) {
+                        // Last column: SUM formula
+                        $firstCol = $columns[0];
+                        $lastCol = $columns[$columnsPerSheet - 2];
+                        $sheet->getCell("{$col}{$row}")
+                            ->setValue("=SUM({$firstCol}{$row}:{$lastCol}{$row})");
+                    } else {
+                        $sheet->getCell("{$col}{$row}")
+                            ->setValue($row * ($colIdx + 1) + $s * 1000);
+                    }
+                }
+
+                if ($withStyles && $row % 5 === 0) {
+                    $sheet->getStyle("A{$row}")->applyFromArray([
+                        'font' => ['bold' => true, 'color' => ['argb' => 'FF003366']],
+                        'fill' => [
+                            'fillType' => Fill::FILL_SOLID,
+                            'startColor' => ['argb' => 'FFD9E2F3'],
+                        ],
+                        'borders' => [
+                            'bottom' => [
+                                'borderStyle' => Border::BORDER_THIN,
+                                'color' => ['argb' => Color::COLOR_BLACK],
+                            ],
+                        ],
+                    ]);
+                }
+            }
+        }
+
+        $filename = File::temporaryFilename();
+        $this->tempFiles[] = $filename;
+        $writer = new XlsWriter($spreadsheet);
+        $writer->save($filename);
+        $spreadsheet->disconnectWorksheets();
+
+        return $filename;
+    }
+
+    /**
+     * Create a synthetic XLS file with many distinct string values
+     * to exercise SST (Shared String Table) parsing.
+     */
+    private function createSstHeavyXls(int $rows, int $columns): string
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+
+        $colLetters = array_map(
+            fn (int $i) => \PhpOffice\PhpSpreadsheet\Cell\Coordinate::stringFromColumnIndex($i),
+            range(1, $columns)
+        );
+
+        for ($row = 1; $row <= $rows; ++$row) {
+            foreach ($colLetters as $colIdx => $col) {
+                // Use varied-length strings with enough uniqueness to populate the SST
+                $sheet->getCell("{$col}{$row}")
+                    ->setValue("StringValue_R{$row}_C{$colIdx}_" . str_repeat('x', ($row + $colIdx) % 20 + 5));
+            }
+        }
+
+        $filename = File::temporaryFilename();
+        $this->tempFiles[] = $filename;
+        $writer = new XlsWriter($spreadsheet);
+        $writer->save($filename);
+        $spreadsheet->disconnectWorksheets();
+
+        return $filename;
+    }
+}