Yeah, its really a stretch. The Royal Dutch Shell guys apparently used a combined efficiency trends + electric car market share to get to a "total mean gas demand" peak. As far as I can tell for poorly articulated arguments, is that it goes something like this: We can model the gas market as the total cars on the road multiplied the average gas mileage per car multiplied by the average miles per car. As a composite number, the average gas mileage is affected strongly by cars which are on the road but use no gas. For each percent of market share which is electric only cars, its equivalent to something like a 3 - 5% reduction in the average gas mileage figure. And total market growth slows, and the percentage of electric cars rises, the actual aggregate demand for gas is going to start going down. Which hasn't happened in a sustained way since the invention of the automobile.