$re = '/<table[^>]*id="table_id2">((?:\s*<tr[^>]*><td>[^>]*<\/td><\/tr>\s*)+)/';
$str = '<table class="my_table" id="table_id1">
<tr class="odd"><td>Line 1</td></tr>
<tr class="even"><td>Line 2</td></tr>
<tr class="odd"><td>Line 3</td></tr>
<tr class="even"><td>Line 4</td></tr>
</table>
<table class="my_table" id="table_id2">
<tr class="odd"><td>Line 1</td></tr>
<tr class="even"><td>Line 2</td></tr>
<tr class="odd"><td>Line 3</td></tr>
</table>';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php