I wouldn't hold my breath waiting for oil to magically reappear in most oil reservoirs.
While organic matter in shales may be currently undergoing diagenisis to form oil, most reservoirs I am familiar with have not exhibited any sort of rapid fillup after depletion. There may be isolated examples where a reservoir is receiving spilloff from another oil reservoir below or maybe even a few cases where enough oil is migrating from huge nearby shale beds to replenish a small reservoir in a few years or decades.
Oil contains the remnants of biological compounds from the source matter from whence it came. If I remember correctly, chlorophyll remnants are there as porphyrins; remants of flowering plants show up as oleanane, etc., etc. Despite Sinclair's old ads, dinosaurs are not major sources of oil; most of it comes from remains of marine and terrigenous (land) organisms found in shale and some carbonates.
I don't put too much stock in Gold's ideas.
Coal beds are often deposited in lagoons near the ocean and are often found near the shales that produce the oil. Organic matter was deposited in a much more concentrated form in the coals than it was in the shales. Both coal and shale can generate oil with burial, but US coals are generally thought to primarily be gas generators.
In general, the deeper one goes, the hotter it gets and the more pressure in situ fluids come under. Over geologic time, the deposited organic matter (lignins, cell wall material, etc.) breaks down into oil. With additional burial, i.e., hotter temperatures, the oil eventually breaks down into gas. Both can migrate to shallower formations and be trapped there.