London Transport

just using my mobile contactless card.

This one.

TfL.gov.uk

But you will need a train ticket to go to Oxford

nationalrail.co.uk

Each person will need their own contactless card or device

I used my Apple Watch for contactless payment the last few trips in London. Saves having to fumble for a card to swipe. Remember to swipe in and out as to not be charged the max fare rate.

I just wanted to mention that the City Mapper App is my absolute favorite for navigating public transport in London.

Thanks all. So I gather there’s no real cost disadvantage to pay as you go vs buying one of those travel cards?

OP: no, no cost disadvantage. And no seven quid (non-refundable) deposit for an Oyster card.

Citymapper is excellent. I also use the TFL app a lot, because it gives live bus arrival times, and I am Queen of the Buses. :-)

So I gather there’s no real cost disadvantage to pay as you go

It’s the cheapest option.

Tap in and tap out in the tube, tap in only on the bus.

For a day trip to Oxford, you can buy an Off-Peak Day Return ticket the day of travel. It will cost around £36. The only stipulation is you have to travel during off peak times, which means leaving London after 9am.

Thank you!!

So, to clarify, I could just use my credit card (contactless option) to pay my tube fare---no Oyster card needed, correct? Thanks!

I also used my Apple Watch, not only for the Tube, but practically everything else in the UK (and a subsequent trip to Italy).
Karen: yes, just use your contactless CC.

I typically use Oyster Card, but I see many people using contactless cards too (both mobile and physical).

Just to make it clear, you use your contactless card to tap in at the entrance gates and out at the exits. The system calculates through which zones you have travelled and charges you at the end of the day, to the same amount as the daily cap, around £8.50 for central London.
You'll need a card each, you can't use the same card to pay for two people.
No need to pay £7 for an Oyster card.

Just a slight clarification on payment cards, you can each load the same credit card onto your phone, and use your phones, or one use the phone and the other the card. You each just need a unique payment combination of device and account.

You also can not tap in with your phone, and tap out with the physical card on the same account, has to be the same device and account.

There is an express bus from London to Oxford, its easy and less expensive. You might take a look www.oxfordtube.com. It runs quite often. The bus is a "coach" so more comfy than a city bus. Plus you can pick where you get off the bus, so perhaps you end up closer to town than the train.

Most Londoners use their credit card to tap in and out. I don't, as I already own an Oyster card, and I really don't want to lose my credit card, not handy when you're a tourist.

Super helpful! I did not know ab the bus. Thank you.