Sometimes a deal almost too good to be true pops up, and you've got to move fast. That's the case with TAP Air Portugal. Word leaked out they are selling 6,600 miles worth of flying for just US$68 earlier today. At the time of publishing, the fare has crept up slightly but is still available via an online travel agency and the airline direct.

Fare available from an online travel agency or TAP Air Portugal direct

InsideFlyer was onto what initially appeared to be an error fare from TAP Air Portugal. Earlier today, they published a story showing you could fly from San Francisco to London Gatwick next June for US$68. There was wide open availability across June and July. Several hours later, the fare has increased to US$82 and is available on most days from May through to August 2021.

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According to Google Flights, this fare is US$255 cheaper than usual, with fare typically varying between US$305 - $790.

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Source: Google Flights

As InsideFlyer notes, buying an airline ticket from an online travel agency (in this case, Gotogate) comes with its own risks. Further, checking in a bag will double the fare. The base $82 fare only allows a carry on bag. For a further $82, you can check-in one 23 kilogram bag. But, if you're traveling light, it's a great deal.

Or you could skip the online travel agency experience altogether and book direct with TAP Air Portugal for a few dollars more. If you are checking in a bag, booking directly with the airline works out a bit cheaper.

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Source: TAP Air Portugal

Why's the fare so low?

While this fare is exceptionally low, TAP Air Portugal has been discounting its transatlantic fares lately. The airline has resumed flying into North America and rolled out new services around Europe. There are seats to fill, and demand is low. Ultra cheap fares are one way to encourage people to fly.

What's also super interesting about this particular fare is that it involves two legs; San Francisco to Lisbon and Lisbon to London. Two planes, two flights. You'd think this would cost more than just taking the first flight from San Francisco to Lisbon.

Not so. Try to book the San Francisco to Lisbon leg only on the same flight on the same day, and it will cost you US$355. But if you just wanted to go to Lisbon, what's the stop you buying the through ticket to London and not boarding the connecting flight?

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Source: Google Flights

What's to stop you getting off in Lisbon?

That practice is called skiplagging (or more formally, hidden city ticketing), and airlines actively discourage it. Across the broader travel community, it divides people. Some people frown upon it as it breaches the rules. Others say, well, I've paid for the connecting flight, it's my business whether I take it or not.

This year, there are plenty of cheap fares already available as airlines scramble to fill seats. If you are prepared to risk it, practices like skiplagging can drive the cost of travel down even further.

For some people, it's a case of make hay while the sun shines. Industry experts don't think fares will stay low once people start to travel again. Airlines have downsized fleets and cut routes. That means there will be less supply than before. When passenger demand exceeds the available supply of seats, prices will rise.

But in the meantime, if you want an ultra-cheap ticket to London next summer, there's now a window of opportunity open to you.