For every qualifying international roundtrip in select United Economy (Y, B, M, H booking classes) purchased and flown before April 15, Mileage Plus members will earn one system-wide upgrade. There is no limit to the number of upgrades that can be earned.
Alas, the upgrade is valid for one-way travel, and qualifying travel cannot include a Saturday-night stay.
Registration is required for this offer. Use promotion code MPW044 when registering.