$re = '/((?<=Sub Total )\d+[.]\d+)|((?<=GST \d\d% )\d+[.]\d+|(?<=GST \d% )\d+[.]\d+)|((?<=Total )\d+[.]\d+)/m';
$str = 'Sub Total 15100.00
GST 8% 1208.00
Total 16308.00
';
preg_match_all($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