- preg_replace: documentation ( source)
<?php
$text = "Oele\nBoele\n\nDus Want\n\nBlaaaaaaaaaaaa";
$text = '<p>' . $text . '</p>';
$text = preg_replace('#\n\n#', '</p><p>', $text);
$text = preg_replace('#\n#', '<br />', $text);
$text = preg_replace('#><#', ">\n<", $text);
echo $text;