Filled up my truck yesterday with diesel from Safeway. Price was $187.9. With my Safeway rewards of $1.00 I put in 19.78 gals for $17.39. Been a long time since I've seen it this cheap.
Fuel prices are mostly dictated by supply and demand. Every year they "budget" what they think will be used in a years time. They refine and store most of that amount. If we have a year to where a lot of fuel is being used (travel, heating oil, etc) the price goes up to try and deter the demand. If it looks like the fuel is not being used up the price goes down to get people to use it up.