This is where the Myth began! Our wonderfully designed planet constantly produces the brown ooze from deep within and up it creeps through any and all debris, organic and otherwise, left behind from times long ago.
Drill Baby Drill - sooner than later. Get the scrubbers in the coal stacks. And stop using the bloody corn for fuel!
We know the planet consists of a large amount of hydrocarbons.
We know that 'gravity' and 'heat' from the 'core' of the Earth make the depths of the planet a giant pressure cooker.
That liquid hydrocarbons would be produced and force their way 'up' through the more solid matter (running away from the heat?) seems to make a lot of sense.