Had this thought while searching the world for oil field biomes.
In many paces, most notably Canada, oil sand mining is becoming more prevalent.
This gave me idea for a Buildcraft oil sands. This would be a normal desert biome where the layers above lava (13+) are replaced with a new block called oil sand instead of cobble, granite, ores etc. The overall aesthetics would still appear as a few layers of simple sand from the surface.
The idea is that the quarry would be used to mine the oil sand, then it would be processed/separated by a new machine, the sieve, into oil and sand. In reality, the process consumes a lot of water so this could be a required input for the sieve. I would say the rate would be 4 or more oil sand blocks to produce 1 bucket of oil. At this rate, even a smaller desert would have massive oil reserves but the low profile would force the payer to find it by prospecting a few blocks deep randomly in deserts(without just scanning with maps or biome finders).

This would result in an extra reward for for those patient enough to do the digging. I think this would be especially nice on more populated servers, where oil spouts close to spawn are wiped out with a quickness.
Anyone with more patience may still find oil without running 10K+ blocks from spawn. The key would be having it virtually undetectable without actually prospecting.

personaly i like the idea and we can definatly look into this at a later stage

currently though we have other things (like the update to 1.12 with all the new things that brings, bugfixes, improvements, ...) we are working on so we will think about this and discuss as a dev team and get back to this at a later stage

Sure thing, bigger fish to fry I understand