How would a dieselpunk world be able to support high oil usage for a long period of time?

The real world has been using oil for hundreds of years and we still haven't hit peak oil yet; depending on population, an Earth-like world might still be far from it. If they had a higher amount of petroleum deposits to start with, they might easily have thousands of years left.

Alternatively, you might consider other sources of usable oil. It doesn't necessarily have to be all petroleum. They might have worked out how to make biofuels from excess biomass (or crops grown for the purpose) using some form of algae or bacterial action.

There's also the option of some form of megafauna or even megaflora which produces usable oil. This could get a bit dark if you wanted it to, since the real-world equivalent for hunting megafauna for oil is whaling and that's a whole mess. But the option is there.

Figure out how many barrels per day they use (there's a lot of data on historical BPD rates online for comparison, and there's probably enough info out there to figure out e.g. how much oil we'd need to replace coal, nuclear, and hydro for electricity), figure out how many BPD they've been using for the past however many centuries, then give the planet enough oil to exceed their needs.

Or don't - peak oil in a dieselpunk setting could be interesting.

Then, figure out how they haven't boiled their planet.

Good question! I've also done some dieselpunk worlds and these are how I dealt with the issue:

• Make the world a watery planet with tons of islands and warm, shallow seas. This site has all the conditions needed to form oil. Since oil is derived from long dead remains of life forms, having tons of warm, shallow seas is best as the depths of the oceans are a terrible place for having an abundance of life. Also, since the remains is mixed with river sediments, it makes sense to have lots of islands to maximize the amount of ocean area in contact with a river. Also, aquatic life forms tend to gather near coastlines anyways (think coral reefs), so you can drastically boost oil forming conditions with a water world.

• Use synthetic oil too. Germany augmented their oil supplies in WW2 with synthetic oil so you could do the same if you feel natural oils won't be enough to make up for the consumption you've envisioned.

• Use more efficient engines. It makes sense that in a dieselpunk world, at least some inventors will try to make engines as efficient as possible. This isn't a perfect solution but it is helpful.

• Use fictional plants and animals and magic. If you are really stuck, you could come up with fantasy life that can generate oil or magic.

Everyone who dies is converted into fuel.

Several years ago, I read an article that our entire concept of the origin of oil may be wrong. The theory was pretty widely ridiculed and debunked, but the concept could very well be viable in your world:

The short version is that oil was not actually created by compressing living matter, but excreted by colossal subterranean colonies of Bacteria that thrive in immense pressure and heat. As such, if an oil rig would be shut down for, say, 50 years then the oil in that location would be replenished as the micro-organisms would have time to excrete more of it.

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The real world does in fact have colossal subterranean colonies of Bacteria in the Earth, in fact they have more biomass than all life on the surface combined. Although they don't excrete oil, but the existence of huge colonies under the surface is not limited to a fantasy world.

I would say make their own oil or use ethanol, or even have an oil producing creature.

They've mastered a way of turning compost into oil. For a horror aspect, it turns out they're using human remains as well.

Shred a whole continent of plants, stuff that waaay down a hole and wait a while.

I like the idea that you make them mine or collect and refine a special resource from, originating from, or being resourced by: the sun 🌞. Only because a Diesel punk world's oil usage would be incredibly high in my imagination, and a sun or similar star or extraterrestrial resource would seem most plausible to support said oil usage. ᕕ( ᐛ )ᕗ