Usually I can make sense of United's fare strategy. But right now, I can't.

I'm flying to Australia with a companion for New Year's. Over the past six weeks, United's roundtrip fares from the West Coast to Sydney, Melbourne or Brisbane have hopped tremendously: They started around $2500+, went down under $1300, boomeranged to $3400, and are outback to $3100+.

Never mind that the flights appear wide-open, with perhaps half of seats unreserved on these leisure routes five weeks out; P9, R9, and XN9 availability across the board (even PZ9 SFO-MEL); and there hasn't been any obvious spike it seat reservations.

More to the point, DL and Qantas are offering LAX-SYD nonstops on the same dates for $1159 and $1180 roundtrip, respectively. That's in Basic Economy, which UA isn't offering on those dates. DL is also selling regular economy for $1359 RT on the dates.

I usually get fare shifts. Here, I don't.