$re = '/(?<=<table>)\s*<tr>\s*<td>([a-z0-9 ]*)<\/td>\s*<\/tr>/si';
$str = '<table>
<tr>
<td>Text A</td>
</tr>
<tr>
<td>
<table> <!-- Notice this is an inner scope table -->
<tr>
<td>Text B</td>
</tr>
</table>
</td>
</tr>
</table>
<table>
<tr>
<td>
<table> <!-- Notice this is an inner scope table -->
<tr>
<td>Text C</td>
</tr>
</table>
</td>
</tr>
</table>
<table>
<tr>
<td>Text D</td>
</tr>
</table>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($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