Alaskan oil that comes in by tanker. Even BC's own oil needs the TMPL to get to Burnaby. It doesn't walk there from Ft St. John.
TMPL also carries refined products to supply BC and Washington State.
Refined product is also trucked in from a refinery in Regina.
Simply put BC and Washington heavily rely on TMPL and AB/SK oil.
It wouldn't cost 50 cents more a litre in Vancouver than AB or SK if they didn't have such a high demand and supply shortfalls in locally refined, domestic and imported gasoline and diesel.
If it weren't for the current TMPL, BC would grind to a halt.