$re = '/\blocation:\s*((?:(?!location:|unit|format).)+) (?:format )?unit (?:(?!location:).)+\b12345566\b/mi';
$str = 'location: Paris format unit no serial no 12345. location: New York format unit no serial no 45764. location: Delhi format unit no serial no 34573.
Location: FD130 New York GA Unit Serial Purchase Order Sales Order Make Model Amount Tax Total 12345566 Location: FD130 Roswell GA Unit Serial Purchase Order Sales Order Make Model Amount Tax Total 0130029964
';
preg_match_all($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