Canada and the Alaska pipeline are the largest supplier of oil to the lower 48, how come the price...?

Question

of oil seems to be determined by sources other than these two?

Answer 1

It is not the State of Alaska or the country of Canada that set the price.  It is the private companies (Conoco-Phillips, Exxon, Chevron, etc) that set the price.  Their job is to get the highest price they can for their product.  When foreign prices rise, they raise their prices.  

Their price isn't constrained by their cost to produce plus some fixed % profit.  Their price can go as high as people are willing to pay.

If you were selling an item on ebay, would you sell it to the highest bidder, or the closest one?  

Conceivable, the USA could nationalize the oilfields as other countries have done (by ignoring the constitutional prohibition against seizing property without compensation).  And then fix prices at a below-market rate.  That seems very, very unlikely.

Answer 2

They may be the largest, but they cannot supply enough to meet all the needs by themselves.