I see several possible explanations, including a long term shift in prices valuing diesel (or "distillate") more highly than gasoline; political pressure to keep gasoline prices low; and integrated oil companies not really needing a high gasoline pricing margin to keep overall profits at an acceptable level. I do not see ethanol as playing a significant role at this time. Regardless of the explanation, refineries and gasoline stations that are not part of oil conglomerates may find this a difficult storm to weather.
The above chart shows that the differential between the retail price of gasoline and the per-gallon cost of crude oil has recently dropped dramatically, leaving a much smaller margin to cover expenses and profit. It is this shift that I am discussing in this article.