- preg_replace: documentation ( source)
<?php
$re = '/\) VALUES (.+?(?=\)))/m';
$str = 'INSERT INTO table (`col1`, `col2`, `col3`) VALUES (\'oneVal\', \'twoVal\', \'threeVal\')';
$subst = ',`col4`) VALUES $1 , \'1\'';
$result = preg_replace($re, $subst, $str);
echo $result;