a nice visual in support of your comment

https://www.visualcapitalist.com/all-of-the-worlds-oil-reser...

That's a terrible diagram. I would have assumed that Iran and Saudi Arabia have the biggest oil reserves from looking at that diagram, since they are front and centre on that visual. Why aren't the shapes uniform?

And where is the legend? What do the colours mean? Why are Libya and China the same colour?

all good questions but you'd have to ask the site that published it.

..i thought it unclear that Venezuela was biggest from the graphic too, had to really stare at it to figure it out.

it seems the colors are continents.