What is this red substance that has accumulated at the bottom of a plastic bottle full of petrol (see picture)? About two weeks ago I put some ordinary unleaded petrol into a plastic water bottle, as a temporary measure (long story, don't ask!). It has now formed a reddish liquid at the bottom of the bottle.

The bottle was emptied prior to adding the petrol, but probably still contained a small amount of water when the fuel was poured in. The bottle was stored in ordinary room temperature.

I presume that the fuel has corroded/reacted with the plastic and left this substance, but I have looked to Stack Exchange in the hope of a more scientific answer...

So, what is the red substance and cause of it?



Please note that the brownish 'slug-shape' is merely an artifact of the light refraction...
Maybe could be some iron oxide or hydroxide from previous storage or ( if you have a iron tap) from it ore maybe directly from the plastic.

Some fuel has red dye in it but I don't think this is the case, because I don't see how it can precipitate.

Maybe it could be a residue of petroleum resin.