Delta Air Lines and WestJet have announced a code-sharing agreement on flights within the United States and Canada, further expanding the partnership between the two carriers.

The code-share flights are available for purchase now for service beginning January 23rd, 2012.

Last year, the two airlines began an interline agreement that allowed customers to purchase connecting flights on one ticket, receive boarding passes for all segments at their first check-in, and tag bags through to their final destination.

Under the first phase of the new code-share agreement, Delta will place its code on WestJet flights to more than 15 cities, while the WestJet code will be added to Delta flights on five markets, expanding the networks of both airlines for customers flying between the two countries.

Members of the Delta Air Lines’ SkyMiles program and WestJet’s Frequent Guest Program will be able to earn miles or rewards on the code-share flights, providing customers another benefit of the enhanced relationship.

“Our code-share partnership with WestJet means an array of expanded travel options in the United States and Canada for our customers, with easy access to the airline’s extensive Canadian network and trans-border service between Canada and the United States,” said Charlie Pappas, Delta’s vice president, alliances.