All well and good Bruce, but there is a variance in your lesson that also needs explaining. Two issues remain; the inelasticity of the products and the availability of substitutes.
1. Gasoline is a product of inelastic demand (demand remains essentially constant regardless of price) and there are few substitutes ......(yet).
2. By comparison, Oranges is less inelastic and there are many substitutes (other citrus fruits) available. Personally I am not convinced of the shortage of refined products has created the need for the price inequities in Western Canada. It does seem that in the past whenever there has been a drop in the price of oil, there is also an instant response of refineries exploding or down for repairs and maintenance.
But I also understand that shortages will never show up at the pumps by specific brand (i.e Shell, PetroCanada, etc) . The retail arm of each of the major oil companies works completely independently of the refineries divisions. With the exception of branded fuels (special products such as Shell's "V" or Chevron's special fuels), all the refineries sell all of their other non-specialized or blended fuels to whomever needs it. So any 'shortages' are spread throughout the entire industry. Clearly I don't have the answers, just a lot of questions......;-)
BTW, you are right, this is probably not the place for an economics lesson.