I am using https://www.heizoel24.ch to find the best deal, but perhaps people here have other tips.
if you find neighbors who are willing to coordinate purchases with you, you can combine your purchase and get significant better per-liter prices due to larger volumes.
Buy off-season (e.g. not during the winter)
No seasonal pattern.
Heizoel24.ch, in my area, only lists one supplier. Checked others one by one individually and found them cheaper than the supplier listed on heizoel24.ch
Larger volume is indeed the way to go.
Would you care sharing some other suppliers? I checked coop and micros and they were both more expensive than the single supplier suggested by heizoel24
oh I just googled my location and Heizöl and went through the results one by one