After buying 3 cheap LHR-SFOs on AA for earlier this year, my sister faced a problem of getting from SFO to YVR. Any flights completed pre 11 Feb. was quite reasonable. $160 or so including taxes. After that, nothing less than USD 235 (close to what she paid for LHR-SFO). Even though the a/c seat assignments looked quite busy (over 60-70% allocated when she bought), she estimated loads were about 30-40%. Maybe AS is trying out getting higher yields with fewer pax. Might work in say, making $70 extra per ticket rather than hardly any on a cheap one. I noticed that UA and AC have become much less aggressive in this market. I've also heard (through here?) that buying through NWA.com might save you some!