Doesn't diesel prices become more expensive that gas in certain times in the year, then lower during others?

I always eye the prices of diesel whenever I'm fueling up my thirst V8. For a while, diesel has been less. Just this week, I saw a few stations where the diesel price was above premium gas.

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2008 X5 4.8
White w/ Black Interior w/ Bamboo Trim | Premium | Sports + 214" | Tech | Cold Weather | Rear Climate | Premium Sound | Active Vent Seats | Heads-Up | Comfort Access | 3rd Row | Aero Kit | Huper Optik Tint | Clear Reflectors