So why aren't lower oil prices being reflected in lower gas prices?

I have finally found a good explanation for why gas prices have not been reflecting the bargain basement price of crude oil in recent months. It is, just as I suspected, mainly due to oil companies fleecing us. More specifically it is the oil refiners who are doing the fleecing, although increasingly, in this age of vertical integration, these are the same people as the oil producers.
With the price of the benchmark West Texas Intermediate crude oil now languishing below $40 for the first time since the depths of 2008, the price of gas and the pump in Ontario remains around $1.07 per litre, as compared to the sub-90c prices of 2008 and 2009 (as low as 70c at one point). With the world apparently awash in record stocks of crude oil, which is the price of gas still so high?
One reason of course is the tanking Canadian dollar, which at US 76c is at its lowest level in over a decade. In an international oil market priced in US dollars, that has hit Canadian prices hard.
But even in US terms, the decline in oil prices in the last year has been around 57%, while gas prices have only gone down 23%, with the discrepancy particularly marked in the last couple of months.
American refineries are operating at or above average utilization levels, which means that, as well as a glut in stored crude oil, we also have a glut in refined petroleum stocks. But this has not resulted in lower prices, which suggests that the refiners are milking the situation and skimming extra profits from the consumer. And indeed it turns out that the so-called "crack spread" (the difference between what the refiners pay for their crude oil raw materials and what they sell it for, effectively the refining profit margin) has been hitting multi-year highs in recent months. This, then, seems to be an unabashed move by the oil companies to claw back at the refinery stage the money they are losing at the extraction stage.
Now, I'm not one to advocate super-low gas prices. I actually think that, for environmental reasons, the cost of high street gas should be kept high enough to discourage casual use. But I would like to see this done through a carbon tax, where the additional income is redistributed through progressive income tax breaks. I don't want the money going to rapacious oil empires, thank you very much.