I'm trying to transport petroleum for making plastic, but I can't seem to figure out the right combination of fluid and/or fuel depots to make the transport drones move petroleum from my refinery to my plastic chemical factories.

Someone please explain to me how to do it like I'm 5 years old.

At your refinery: place fuel depot (if you don't have any placed yet, in other place perhaps), connect it to petroleum gas - it's needed to supply your requester depots with fuel. Place some drones here.

Also at your refinery: place fluid depot, connect to petroleum gas - that serves as a supply/source for requester. No drones required.

At destination: place requester depot, select petroleum gas. Place drones here, the more drones - the more and faster they'll deliver. They'll wait for drone from fuel depot, then start working.

All 3 need to be connected by roads, preferably 2 tiles wide to enable faster low-resolution pathfinder.

Thank you so much. Exactly what I needed. Will try this later today.

chugin: really nice and compact description. the following is a bit longer and not needed in most cases anyway, but it's a hint for some additional finetuning for the "worst case", probably "overenginered" a lot :

when the factory runs low/slow on petrol, the following "worst case scenario" might happen: petrol is delivered to plastic making and not enough is left for the fuel depot. thus after a while (guaranteed to happen sooner or later if petrol is low/slow) also plastic production stops since also that petrol requester runs out of fuel. at this point (or earlier), the petrol provider will fill up and finally also the fuel depot will start filling up again, and petrol fuel will be delivered to requesters. again the worst case might be that only a few requesters get fuel, and that those are the petrol requesters for plastic production, and thus they start transporting petrol for plastic production again, letting the fuel depot fall dry again before all other requesters are fueled up too. but that is only the worst case and can only happen when the factory is really low on fuel, and even then sometime the plastic will stop being needed and fuel starts being delivered again. thus (although at a very low rate) everything will still work "somehow", unless you transport also the oil (to make the petrol) with drones :-)

to avoid similar problems, pumps can be used between the petrol generation and the depots to give priority to fuel: connect the petrol production to a pump, that pump to a storage tank (not only as an additional buffer, but mostly to be able to measure whether there is petrol available since the fuel depot itself can not be connected to the circuit network), and finally that tank with the fuel depot. the pump can either run all the time, or you can connect it to the tank and shut it off by a condition (eg "enable if petrol<5000") to not unnecessarily fill that storage tank. a second pump between petrol production and the petrol provider can then be turned on only after enough fuel has been provided to the fuel depot, and otherwise shut off (eg connect a wire to the same storage tank and use a condition on the second pump like "enable if petrol>=3000").

this entire setup should not be needed in most cases, but it should guarantee that even in the worst case (!) the fuel depot has highest priority to always have 3000-5000 additional petrol (in addition to the 10k that can be in the fuel depot) available to fuel requester drones at all times, and that petrol (for use like plastic or red circuits) only will be sent to requesters when there is at least a buffer of 10k+3k fuel/petrol.

Thanks to both of you, everything is working smoothly now :)