Twice I have been on domestic flights where airlines have offered last-minute, at-the-gate upgrades to business and/or first class. In September, we are traveling from Chicago to Beijing, and in early October from Hong Kong to Chicago -- both on United. Has anyone ever seen or heard of at-the-gate upgrades to business class offered for international flights, especially on United. The flights we are booked on have over 50 business class seats available as of today. We are willing/able to spend up to $1,500 extra each, would love to fly business class but can't spend the huge difference that is available right now.

Its common to see upgrades on domestic flights, usually to frequent flyer members. Its really rare to see it on international flights. The only time I have heard of it happening is when the front cabin is undersubscribed, and the back cabin is oversubscribed and enough people show up that they would be forced to bump people from the back cabin. Its called an operational upgrade, and I always volunteer, but without success so far.

It may be more common now, as with the route consolidations and sharing of aircraft, its not uncommon to see the back cabin absolutely stuffed.

I'd research/ask this question on the United forum at flyertalk. I think I recently saw something there re: purchasing upgrades at checkin for a transatlantic flight, but there are many frequent transpac fliers on that board who will have some idea how likely this is to come up.

And there are non-rev waitlisted that only employees can see.

How do you know that 50 J seats are available?

I suspect that you see that on ua.com seat map. Seat maps are nowhere near in accuracy of how many seats are available.

If you tell me the dates I will check the loads on your flights and only then I can possibly make an educated guess at best, of what's going to happen.

As somebody above already stated. The only time most airlines including UA will offer paid upgrades is when they are squeezed for room in the back. Instead of bumping people and paying compensation, or giving free op-ups, airlines will "offer" a paid upgrade to anybody that wants to take them up on it. The amount you are willing to spend is good enough, but if the economy class is not oversold I doubt very much they will offer upgrades at the airport. That's what's called "product devaluation". If all airlines did this on a regular basis, then most people would not purchase the more expensive J ticket and just arrive at the airport early to snag a seat at a bargain. The airlines can't afford to play this game regularly if they hope to get more $ for their J and F seats.

So, it does happen, but never count on it.

Then again, I have been wrong before.

Last fall, when I checked in at a kiosk for a United flight from Dulles to Buenos Aires I was offered an upgrade from my T fare to business class for $550.

In May, I was upgraded, without asking, for free at the gate both ways between San Francisco and Nagoya. This was a $629 roundtrip from Dulles. Was upgraded to first from SFO->IAD using 500-mile certs. I have the status of (fast-tracked) Mileage Plus Executive.

You could take a look at the Ameniti program that United has. You pay $195 or $295 and can get free companion tickets when you buy regular business or first class tickets. Looks like one ticket would cost about $7200.