None other than Kenneth Deffeyes of Hubbert's Peak fame.
In Beyond Oil: The View From Hubbert's Peak Deffeyes writes:
Burying the sediments, or the oil, deeper than 15,000 feet continues the molecular breaking until the remaining product has only one carbon atom per molecule. That gas, almost pure methane (CH4) is often referred to as "dry" natural gas. The limit of 15,000 feet is the bottom of the oil window. If you are looking for oil, you need organic-rich sediments that have been buried, at some point in their history, into but not deeper than the oil window.This makes one wonder what kind of drugs Deffeyes is on. Transocean, the world's largest deep water offshore driller, regularly drills oil wells, not natural gas wells, twice as far below the "oil window" claimed by Deffeyes. And they are going deeper looking for oil, not natural gas.
Also see The Many Wrong Predictions of Ken Deffeyes.