Originally Posted by jsloan

UA does occasionally, but very rarely, confirm mileage upgrades at the time of booking. They're somewhat more available on long-haul flights than they are on short-haul, but even then confirmable inventory is diminishing. As you noted, the required copay makes it a terrible use of miles anyway.

United offers last-seat availability for awards, but they can be a large number of miles. How are you searching? I'm having no problems finding flights for nonstop routes from SFO -- they're just really pricy in some cases. Can you give a sample route and date?