As far as I understand, there are no clipper card vending machines at Oakland International Airport (OAK). But there is one at Coliseum Station. If I plan to buy a clipper card anyway, should I do that at Coliseum Station? Or should I buy a regular ticket from OAK to my destination in downtown San Francisco and buy a clipper card afterwards?
There are Clipper machines at "virtual OAK station"
- Board the BART-OAK cable car*. There will be a conspicuous lack of fare-gates or entry controls. You will fear this is a proof-of-payment system. It's not. Don't worry about it.
- Exit at Coliseum Platform 3.
- There is nowhere to go except through fare-gates or back to OAK!
- Buy your Clipper card(s) right there.
If you intend onward travel on BART, tap through the fare-gates, and you are now in the paid area of BART. Where to go next will be obvious. Your card will be encoded as having entered the BART system at OAK Airport.
If you do not want to ride BART today, buy your Clipper tickets and hop right back on the cable car for a free ride back to OAK. This is legit. It's quite fast, and you could do it while your companions collect luggage.
How does that work? BART is a variable-fare system, meaning you must card-in when you enter, and card-out when you leave. However, the OAKland Airport cable-car is a simple 2-station shuttle, and for design-geometry reasons, the Coliseum end empties only into the paid area of the BART station at platform 3. There's no way to get landside from platform 3. So BART displaced the OAK fare-gates to the Coliseum end. Now they do not need to staff the Airport station.
Since the fare-gates are there, so are the ticket/Clipper sales machines.
Joyriding the BART system proper
BART has an "excursion fare" intended for joyriding the BART system by entering and exiting the same station. Normally this is overpriced, but from the Airport station it's the cheapest fare to anywhere, at $6.
So if you want to joyride BART proper, you can enter the faregates and take the normal BART trains. Complete your joyride within 3 hours or you'll have to see the agent and accept a stern look.
The Dublin line is easiest to access and it's #2 for scenery.
The Fremont line is just more of what you see on the boring part of the Dublin line.
The scenery king is the Pittsburg/Bay Point line, but you must change trains to reach it (this isn't too bad though).
San Francisco line is dead last for scenery as it's all underground west of Oakland. The cool spots east of Embarcadero are the railyards and the Imperial Walkers (really) at West Oakland and the black coolness of the Transbay Tube.
Richmond Line, only the far half is scenic, and it's a long drag underground through downtowns Oakland and Berkeley to get to it.
The short trip is a bounce to East Dublin and back. The longer trip is to Embarcadero then Bay Point then Macarthur then Coliseum, but that's ambitious if you only have 3 hours to kill.
Walking off the airport property is out of the question because it's miles, so Uber would be required. The Hegenberger area is pretty desolate but it has an In-n-Out Burger (thanks Zach Lipton).
The town of Alameda has back-road access to the airport and is very nice. Consider either its Park St. downtown (over 100 shops and local eateries) or South Shore mall (fast-casual food). Either one is a 10 minute Uber from the airport.
* Yeah. It's really a cable car. Not quaint, but modernistic because BART. It doesn't have a grip or gripman, and the cable is permanently bolted to the car, unlike the system across the bay. The cable stops and starts to move the car. You can watch the sheaves turn at the OAK end; that's the powerhouse.
For travelers landing at OAK, there is no need to purchase a BART ticket or Clipper card until after you arrive at the Coliseum BART station Platform 3, where you can buy a BART ticket or regional Clipper card from vending machines.
The BART line between Oakland Airport and Coliseum Station is a people-mover "monorail" service (though it actually has two rails). To get anywhere from OAK, you have to transfer at Coliseum to the regular heavy-rail BART system, and you can buy your Clipper card there. It's not clear whether it would even be possible to buy tickets of any kind at OAK itself.
If your trip is at least 10 days away, then order a clipper card online (or by phone) and get it by postal mail (in the United States). It's also the cheapest way to get a card because it's free if you opt-in for autoloading money on it (you can always opt-out after you receive it). Otherwise, a card is $3.
Note that the fare for the OAK to Coliseum BART extension is $6 just for that little spur line (prices checked April 2019). Depending on the number of people in your party, it may be cheaper to take the Uber. It’s definitely cheaper to take the 73 AC Transit bus from the airport to Coliseum as the bus is only $2.35.