I will travel from Chicago (UA) -- LA (UA) -- Melbourne (Qantas) -- Adelaide. I believe I will need to pass immigration at Melbourne. How does Qantas handle checked baggage from a non-OneWorld airline? Qantas seems to have more restricted carry-on luggage policy than UA?

One my way back, can I cehck luggage all the way to ORD?

Thank you

A lot depends on whether everything is on a single ticket, or whether you have separate tickets for UA and QF.

If everything is on the same ticket, then the bags should be checked to the final destination (in both directions). Nonetheless, you would need to claim the bag in MEL and clear customs, then go upstairs and drop it off with Qantas. Same in reverse - bag should be checked through to ORD but would need to collect in LAX and clear customs.

If you have two separate tickets, then QF will only check your bag to MEL on the way back. You would need to claim the bag in MEL and check in with UA as though you were originating in MEL. On the outbound, it would be whatever UA's policy is - I would guess they only check it to MEL, but procedurally this doesn't change much since you need to claim, clear customs, and go upstairs to Qantas anyway. The key differences on a separate ticket are (a) the allowance is independent for each ticket - QF will re-weigh the bags in MEL and if overweight or too many pieces per QF's domestic allowance, you would be charged; and (b) the connection is not protected, i.e. if the UA flight is late, QF can treat you as a "no show" and do not need to accommodate you.

So please clarify whether your travel is on a single ticket or separate tickets.

Carry-on is a different story - you are not entitled to extra QF carry-on simply because of the UA connection, irrespective of whether your travel is on one or two tickets.