How do Toads in Naruto produce Oil? Toad oil as shown on Mount Myoboku was produced from a special fountain that allowed user to more easily feel the natural energy around them. This was used in the initial stages of Senjutsu training by Jiraiya and Naruto.

However, We've seen several combo jutsu's used by Jiraiya which rely on the Toads spitting Oil (Toad Oil Bullet). Which can be lit on fire or even mixed with both Wind and Fire Jutsu. We know toads can manipulate Chakra and are mostly affiliated with Water Style.

So Is the toad oil produced naturally in the Toad's stomach's or is it something that they achieve by nature manipulation (manipulating multiple chakra natures, similar to Kekkei Genkai)?

Update: I understand "Toad Oil" based techniques utilize chakra, but the source of the oil is not explained. I have read the wiki entries and Wiki just states "converts Chakra to oil" but doesn't explain it. Is it like the Dragon Flame produced by Dragons? For an in universe example take a look at Katsuyu and her/its ability. I can see Slugs producing Slime and Katsuyu using that slime similar to that of the Mizukage's Acid Release. This is both a Nature transformation and Kekkei Genkai, while also possible naturally. Do toads naturally produce this oil, do a nature transformation, Is there any myth that attributes toad spitting oil etc. is what my question moves toward.

Additionally, for those confused about Ying-Yang techniques and Nature Transformations should go through the wikia page and read the cited information! Naruto Wikia - nature Transformation


  Aside from the five elemental nature transformations, there is a second kind of nature transformation that are the source of all non-elemental techniques such as the Shadow Imitation Technique, Multi-Size Technique, medical ninjutsu, genjutsu, etc. There is Yin Release (陰遁, Inton), based on the imagination and spiritual energy of a shinobi, and Yang Release (陽遁, Yōton), based on the vitality and physical energy of a shinobi. Together, they are used to perform Yin–Yang Release (陰陽遁, In'yōton, Onmyōton). 


You can't just club any random technique to be Ying/Yang.

Additional Update: Trivia section of Wikia for the Nature transformation gave an interesting lead.


  Techniques such as the Toad Oil Bullet and the Poison Mist mention "converting" or "kneading" chakra into materials or substances, but have never been mentioned to use certain chakra natures. 


So I think I am not the only one unsure how these techniques are performed!
The Toad Oil Bullet Is a skill used by Jiriya that converted his chakra into Toad oil. He spit out a volume of oil more than his body's size, proving that he could not have stored it inside his body. So the answer appears to be that there is a technique that converts chakra to Toad oil.

However, It is entirely possible the Toads, especially Larger ones, can swallow toad oil and regurgitate it later to conserve chakra usage required to create it. 

It is notable that the Toad oil they spit out and Toad oil used in Senjutsu training might be different oils. The wiki entry on Mount Myoboku notes:


  There is a sacred fountain on Mount Myōboku which produces a special oil which allows people to more easily feel the natural energy around them


So it seems only the fountan produces the Sage Mode oil. Also, the Sage Mode oil looks significantly like cooking oil, very light, clear, and of the same consistency, while The oil spit out to be ignited looks dirty, and dark, sometimes even opaque.

Edit: addressing your edit, There is only one thing that could possibly be added, and its a Theory.

You copied one line from the wiki on the trivia section of the Nature Transformation page. However, the very next line gives off a HUGE hint.


  Certain other techniques involved in manipulating substances are also often confused to be chakra natures, such as silk, bone, and ink. However, these substances cannot be produced from chakra alone, meaning the chakra is not changed in nature, and it is rather used to change already-existing substances.


The oil is called Toad Oil, So its could be some kind of substance a Toad can naturally create. If that is the case, then this would literally be exactly like Kimimarus Bone based Jutsu, Shikotsumaku, or Kidomaru's Spider Technqiues. Just like how They can take the natural substance that already exists (bone/Spider Silk) and use Chakra to create more of it, Toads would do the same. Perhaps that is what Kneading into a substance means, Mixing Chakra with a substance, and converting the chakra into more of that substance. Since everyone who uses Toad Oil is either a Toad, or Jiriya after he goes Sage mode and becames part toad, then they would likely have a natural source of it to duplicate via Chakra kneading, if that is indeed the case.