If this is an MS-SQL server then the "default" order is likely to be the order of the clustered index. However, relying on that ordering when using an RDBMS is unwise, as it could change at any time, or be different if you move your script from one type of database server to another, or if other DDL changes (such as different indexes, different locking methods, etc) are applied.

In short - never rely on the order of data in a SELECT without an ORDER BY clause.

Michael