Oracle has, for a long time, led the way when it comes to handling the databases of large companies, with over half of all Fortune 100 companies in the US using Oracle for their primary databases back in 2002. The reason for this is simple: Oracle is the most advanced, and also the fastest database system out there. However, it is also one of the most expensive software solutions any company will ever buy. Back in 2001, Oracle cuts its prices substantially, and one company was "happy" to report that running Oracle on a machine with just one CPU now "only" cost just over $80,000. Of course, what you pay depends on how you license it - there are less expensive options.
Although Oracle is very pricy software, it is undoubtedly the best. Nothing comes close to offering the same level of reliability or security, whilst still managing to out-perform their competitors.