United is offering up to 15,000 bonus miles for roundtrip flights to Australia from the U.S., Canada, Puerto Rico or U.S. Virgin Islands from March 1 through April 30, 2006. Registration is required.

• 15,000 bonus miles for purchasing and flying a paid, qualifying roundtrip in United First® (F fare only)
  
• 10,000 bonus miles in qualifying United Business® (C, D fares only)
  
• 7,500 bonus miles in qualifying United Economy® (Y, B, M, H fares only)
  
• 5,000 bonus miles in qualifying United Economy (Q, V, W fares only)

(No bonus miles are offered on the absolute lowest — S and T — fares.)

Partner and code share flights don’t qualify for the offer. Tickets must be electronic. Miles should post 6 to 8 weeks after completing the return flight.