Based on jad's tip about Top Tier, I vif isted the site and saw that there are companies in Canada. Since its regular fuel (87 octane) is about 4 cents/litre cheaper than "the rest" and its 91 octane is only 10 cents/litre more than that ('the rest' usually charge 15 cents/litre more), I sent a general question to COSTCO Canada HQ in Ottawa (just down the road from where I work) asking:
a. from whom does COSTCO get its gasoline; and
b. would COSTCO Gasoline qualify in the Top Tier program (I included the link)?
The next day I received a reply stating:
a. there are only 15 refineries in Canada to supply gasoline regardless of
brand name; (this did not surprise me as I knew this already); and
b. COSTCO gas is unbranded, meets the minimum standard set by the Canadian
government, and has no additives thus it could not meet Top Tier requirements.
That said, I have no problem throwing a bottle of injector cleaner every 5 tankfuls or so since the car runs well on COSTCO gas and, in addition to the better price, if I use my COSTCO AMEX/Membership card to pay, I receive a 2% rebate annually to spend in the warehouse.
As for the reference to BP gasoline in the owner's manual, I suspect that it likely reflects the UK and/or Europe and not North America though I stand to be corrected.