Transit card

I don't know what London's Oyster card is, but i can tell you your options in Budapest.

There are individual tickets for 350 forints each or ten for 3000 forints

There is the Budapest Card. If you plan on going to a bunch of museums and the zoo and spend a lot of money in tourist shops, it might pay for itself.

Budapest Card for 24 hours HUF 5,500
Budapest Card for 48 hours HUF 8,500
Budapest Card for 72 hours HUF 10,900
Budapest Card for 96 hours HUF 14,500
Budapest Card for 120 hours HUF 17,500

And there are TravelCards. They are real bargains.

Budapest 24-hour travelcard HUF 1 650
Budapest 72-hour travelcard HUF 4,150
Budapest 7-day travelcard HUF 4 950

Most can be purchased in vending machines, but the 7 day TravelCard requires you to go to a ticket window and show identification.

Oh, the Budapest Card is for this: https://www.budapestinfo.hu/budapest-card

While tickets and TravelCards are for travel only.

If you are in Budapest and needing transit for four days, note that 7 day pass is a better value than an 72-hour plus a 24-hour pass. You will need ID to purchase it and have ID to show when using it. Deak Ter, for one, has a ticket office for purchasing a 7-day. You basically cannot get on a metro line without a ticket as attendants check everyone entering a subway gate. In six days in Budapest last month only once was there not an attendant waiting to check us. So carry your ID if you buy a 7-day or validate your tickets. We were never checked when using a tram or bus but the fines are high and ticket prices are cheap, so follow the rules.

Earlier this month we spent a week in Budapest and we were only checked twice, so it can vary. You can also be approached on a bus or tram or in the station by a plainclothes metro cop wearing an armband. The fine is 8000 forints on the spot. When you purchase a book of 10 tickets, you will get 11 identical slips of paper. One is a receipt. Don't get confused and use it as a ticket.

I've stayed 4 and 5 days in the past 2 visits and always get the 7 day pass, better value--once at the airport and this past month at the Keleti station. It's always checked at the metro but only once on the bus, and I rode the bus quite a lot this time.

I've seen it a lot lately, there are days they just don't check; other days they get you coming and going. My significant other was joking she was upset because we paid good money for the cards and they damn well better check them. Over the years we have been checked getting on the metro, and getting off the metro. One time we were pursued through the underground at Nyugati, way beyond the security point, by a plain clothes metro cop. One time on the 4/6 tram a man pulled out his arm band, put it on and started questioning my daughter in Hungarian. She gave him a go to hell look and I had to step in before it escalated. My daughter is sort of like Fred when it comes to strangers. We also got caught once using the receipt as a ticket (by error), that was the only time we ever got fined.

For ease I got some of these to carry the cards (they are really just flimsy paper): https://www.amazon.com/gp/product/B071D55VN9/ref=s9_acsd_newrz_hd_bw_bljZEp_c_x_w/136-4951048-2592126?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=merchandised-search-5&pf_rd_r=80XJFTNW862PGWHJ9N73&pf_rd_t=101&pf_rd_p=c4cbc2ba-c0c0-5e8a-b3df-4f05b6b07035&pf_rd_i=705348011

James--good idea for the cases. I keep mine in a handy pocket of my purse, then it comes home with me and I set it on my dresser or desk as a little memento of my happy place. My increasing understanding of Hungarian came in use this trip, I was slightly jostled by the ticket checker on a crowded tram and as I turned and gave him a fierce look he said "bocsanat, blah blah blah, jegy-something" and I realized he wanted to see my ticket.

I'm trying to understand the pass purchase/use process (say, the 72 hr pass). On the BKK ticket site (bkk.hu), 4 types of ID are listed that can be used with a pass. Quoted from the web page:

For full-price passes:
- BKK pass ID
- VOLÁNBUSZ-BKSZ pass ID (only for the Budapest pass)
- Personal ID card
- Card-format driving licence

Is a passport an option? ("Personal ID card"). Or a US drivers' license?

Twice I've bought the 7 day (hetijegy) pass and that's only sold at a ticket window, at airport or Keleti. They ask to see your passport so they can spell your name correctly on the pass, from what I can tell--airport asked for passport and Keleti just had me write my name out for her. The other types of individual tickets and fewer day passes can be bought from machines. You won't need to be showing anyone your ID when using a transit pass, just hold it out for the checker as you enter metro or get on bus or tram.

The 72 hour TravelCard requires no identification and can be purchased at most metro stops at windows and from the vending machines. The 7 day TravelCard does require identification as it bears your name to prevent sharing it,

The travelcard is to be used by one person only as it is personalised
and non-transferable. Before use, the name or the number of the
general BKK pass ID or student ID or a photo ID (e.g. identity card,
passport, card-format driving licence) of the holder is to be provided
at the time of purchase as it will be printed onto the card. Upon
request of the inspector, please hand over your travelcard along with
the matching ID.

I have purchased them at the Deak Ferenc ter metro station. I hadn't considered you couldn't purchase them at any window. Don't know the answer to that. As for which ID to use, do know that Hungary does require you to carry your passport on your person at all times.

You will have to show the card when entering the Metro an sometimes when exiting the Metro; and whenever requested by a uniformed or plain clothes inspector.

According to the BKK informational PDF they now offer a "5/30 BKK travel card" which is for 5 selected days within a 30 day period. It is HUF 4550 (vs 4150 for the 72 hr card).

As in Prague, when we got to the kiosk to purchase the transit card, the nice lady waved me away. I explained that I was carrying a US passport -- that only my husband's was EU. No matter, she said, just go ahead.

We passed through 4 metro gates -- 4 inspectors. Not a hitch. So it appears that a US (or EU) passport is all that's needed for BKK system travel in Budapest for those over 70 yrs.

Excellent. I hope everyone sees it that way. It would be terrible if you had to pay a fine; and the metro cops don't screw around. No talking your way out of it. For instance, US student Id's don't always get you a student discount at a museum; depends on the clerk.

But I am happy you were treated well. .

More than you ever wanted to know about Budapest public tranportation:

http://gotohungary.com/documents/183786/12531594/BKK+brochure+ENG_A5_20141018_web.pdf/fc026e0e-7b05-4c45-9011-9dbf3f0c8db3