A number of ways spring to mind, but as for the most efficient that depends on your hardware, network and setup.
Solutions would be replication (Oracle can be a publisher), standard SSIS Oracle Source SQL Destination data flow tasks, BCP Out from Oracle, BCP In to SQL or SSIS In to SQL, linked servers.
Again the list goes on so it would be a case of pick a couple of ways and see what works best for your environment.
How to post data/code for the best help - Jeff Moden[/url]
Need a string splitter, try this - Jeff Moden[/url]
How to post performance problems - Gail Shaw[/url]
Managing Transaction Logs - Gail Shaw[/url]
Troubleshooting SQL Server: A Guide for the Accidental DBA - Jonathan Kehayias and Ted Krueger[/url]