How can I make a thick, gooey brown substance that I can drink by the mouthful.
There are some questions one simply should not ask the internet.
More seriously, two questions:
1) What kind of oil are we talking? Thick and gooey is fine and well, but are you after that golden, translucent, brand-new-bottle texture, or something darker and gloppier?
2) How close is your audience? Does the effect need to be bang-on accurate, or can you fudge it a bit?
One option worth considering is getting some water of the appropriate colour (Black food colouring is available, but can be rough to find. Google can help you make it yourself, if necessary.) and adding a few drops of a thickening agent like pectin, xanthan gum or agar, although you'll need to do some experimentation in order to get the ratio right. The major benefit of going this route is that the product should be both shelf-stable and fairly flavourless. (I imagine it'd be
unpleasant to pour down your throat, but it shouldn't taste like anything other than the water which went into it.) Do bear in mind, though, that these thickening agents are usually used to prepare jellies and jams, so you should only be using a teeny tiny bit if you want the liquid to remain a liquid. You want to get rid of some of the viscosity, not eliminate it altogether.
If flavourlessness is a problem, you could toss in a few drops of essence of peppermint or cinnamon or whatever else to make it a little more appetizing without having to go the sweet route. (And that's
culinary essence-of-peppermint/cinnamon/etc., not the stuff you'd buy for aromatherapy.)
