Avis and United have a new offer:
Rent with Avis on your next trip. You'll save up to 35% and earn 75 MileagePlus® award miles per day – plus 150 online bonus miles – when you book your rental through United® and use United's Avis Worldwide Discount (AWD) number K019376.
Plus, you'll earn even more miles the longer you rent – up to an additional 2,000 bonus miles on rentals of five days or more at participating airport locations around the world. Use coupon number MUAA125.
This offer is certainly not as good as the 3k per rental Avis offered with American Airlines last summer. However most of these car rental promotions are only available domestically and not for international use. However this one works for all participating airport locations.
I just applied the bonus ID for an existing, upcoming reservation in March in Berlin, Germany and it worked just fine.