Not only that, in France for example the liter of Diesel fuel was always 10 to 15 euro cents cheaper at the petrol station due to how regular gasoline and diesel fuel was taxed.

That's why before EVs started to show up on the market en masse if you walked into a dealership they would always recommend that you pick the diesel engine if you wanted to save money of fuel costs.

That was actually the reason why the Yellow vest protests started in 2018 when the French government announced that the taxation gap between diesel and regular gasoline was going to disappear gradually.

Small edit to add to the context:

By that point, when the protests started in 2018, the governments(right and left) of France and the many French automakers had been pushing diesel engines as THE solution to alleviate rising fuel costs and so justifiably, the protesters thought that someone had just pulled the rug from underneath them.

Also this measure was in direct contradiction to Macron's campaign promise which was that he was going to reduce the tax burden or at least not increase it on the middle class, especially the rural middle-class that basically cannot get a job without having a car as public transport is almost non-existent in rural France.

That and many other things which I won't get into since it is not relevant for this discussion really riled people up.

In Canada, diesel fuel is priced around mid-grade gasoline (89). So it's slightly more expensive than regular, but slightly cheaper than premium (91/93).

Based on this, I've always thought of diesel as "more expensive", like you better get 15% more power/miles out of it if it's going to cost more! However, I suspect that most people purchasing diesel vehicles have as their other choice a car that would slurp premium, so for those buyers perhaps diesel is still a discount, even in Canada.

Diesel is less fuel efficient than regular gasoline except when you measure by volume. It gets fewer miles per unit of energy in the fuel.

Can you source that? Diesel is only 13% more energy dense than gasoline [1] so the difference between the two fuels isn't huge.

I suspect that modern (last five years) turbocharged gasoline engines are probably approaching diesel thermal efficiency, but I don't think that it's correct to say that they generally surpass it. The gasoline Ford EcoBoost is 33% thermally efficient while a BMW N47 turbo-diesel is 42% thermally efficient, as an example [2].

[1] https://afdc.energy.gov/fuels/properties [2] https://en.wikipedia.org/wiki/Brake-specific_fuel_consumptio...

The fundamental difference in how the engine operates by throttling fuel only instead of air and fuel accounts for a large fuel economy savings

Fuel is sold by volume, which is why volumetric fuel efficiency is desirable to the consumer

Fuel is sold by volume and fuel type; diesel is about 25% more expensive per gallon than regular gasoline where I am.

Correct - where I am it is cheaper most of the year, a bit more expensive in the winter.

And it is 10% cheaper than gasoline where I am (South-Africa)

Yes, but measuring miles per volume of fuel and setting increasing targets was a big focus of reducing petroleum dependency since the 70s.

The focus has more recently shifted to reducing overall emissions of CO2 and other harmful gases and particulates, which makes diesel much less appealing.

I don't think any car buyer has ever looked at Calories per litre of fuel as a relevant metric for purchasing.

People that buy cars almost exclusively care about cost of fuel to move between A and B.