The answer could be different depeding on the operation being performed. In Oracle there are many different types and levels of locks, and some operations would cause one type or level of locks while other operations would cause a totally different set of locks.
In general, there are two basic types of locks, which are ‘exclusive’ and ‘share’.
Exclusive locks are obtained to modify data, and only one transaction can put an exclusive lock on a resource at the same time. In common DML operations such as UPDATEs, exclusive locks occur at the row level.
Share locks are less restrictive, and many different transactions/users can put a share lock on the same resource at the same time.
These types of locks are not mutually exclusive. Some operation could put exclusive locks at the row level, and a shared lock at the table label.
The benefit of row-level locking ? Higher degree of data concurrency .
Here’s a better and more detailed explanation:
<a href=”http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/consist.htm#i5704″>How Oracle Locks Data</a>