Is Return Flight Same Plane?
 

Doing a mini MR from ORD-OAK. Departing on Flt#531. Returning on Flt#752. Is there a way to determine if the return flight is the same plane in case my departing flight is delayed?

Use flight status to see if the arrival gate for 531 is the same as the departure gate for 752. Not definitive (depending on how much time there is between the flights), but a good indication.

You can also check schedules to & from OAK. If there is only one flight arriving and leaving with a particular metal within a long time frame, then likely to be same a/c.

Not the same aircraft ...
 

... unless you're travelling on a Saturday.

Weekdays through the end of October:

UA531 ORD 9:55 AM OAK 12:23PM 752 4h28m
UA752 OAK 1:28 PM ORD 7:30 PM 319 4h02m

Saturday, October 28:

UA531 ORD 9:55 AM OAK 12:23PM 752 4h28m
UA752 OAK 1:33 PM ORD 7:32 PM 752 3h59m

No other 757s come into OAK around the noon hour, so it's 99.99% certain to be the same aircraft on Saturdays.

Hm, it'd be interesting if they were, actually... ;)