$re = '/[IO]\d{3,}(\w{12})/m';
$str = '2:O5641057130214TESTBIC34XXX26264938281302141757N
2:I101YOURBANKXJKLU3003';
preg_match_all($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