Many are complaining about fuel prices going up because of the war on Iran, but prices were already high because of high taxes:

• US fuel taxes make up 20+% of the price
• European fuel taxes make up half of the price
• It appears 7.6% of the German government’s revenue comes from fuel taxes.

You can avoid these taxes by making your own diesel at home, potentially saving money while reducing waste and being less dependent on geopolitical affairs.

Biodiesel is easy to make from new or used vegetable oil and can be used instead of diesel in 21st century cars.

• Short version: https://www.wikihow.com/Make-Bio-Diesel
• Long version: https://www.dudadiesel.com/biodiesel.php

If you want to save a lot of money, ask restaurants for their old cooking oil cheap or for free. Biodiesel can also be made from animal fat, which is cheaper than vegetable oil, but there are fewer guides on the process.

Diesel can also be made from used motor oil if you have a centrifuge and a still for distillation: https://carobjective.com/how-to-make-diesel-fuel-from-used-motor-oil/

How to make a simple still from a pressure cooker, copper tubing and bucket: https://www.instructables.com/How-to-make-a-still/

Making a fractional distillation column isn’t that much harder: https://www.instructables.com/Build-a-Lab-Quality-Distillation-Apparatus/

With this you could potentially separate crude oil into various components and use them for both gas and diesel cars, stoves, heating, oil lamps or sell them. Small sellers may be exempt from taxes depending on where you live.

For gasoline you could also try the ideas here, although they seem to be expensive or impractical for road users: https://www.wikihow.com/Make-Synthetic-Gasoline