In Europe there are really two realities: the land of the living and the land of the dead.
In big cities such as München, Stuttgart, Hamburg, Berlin, Paris, and London the birth rate is higher than the death rate and the population is rising.
In small towns and rural areas the death rate is much higher than the birth rate and the population is falling. Mainly this because there are very few young women in such places, and there are high numbers of retirees taking advantage of lower cost real estate. Rural workers and economies are of little use in an information and science based economy anyway. In Germany large parts of the country will eventually go over to forests and farms with very few people living there. This is alarming to some people, and will make Germany’s aggregate population fall until the rural areas and small towns decline to nothing, but it is not harmful to the economy.
As urbanization becomes more intensified demand for oil will fall even without improvements in technology. Urban infrastructure is far less energy intensive per user than rural and small town infrastructure, and can be improved to use even less oil with more investment. Money follows people too so this is really quite easy. As this goes on oil demand in the rural areas and small towns will decline to negligible levels over time.
In the USA such a thing is going on too, and will become especially pronounced as the population age. Although for the USA things are complicated by the enormous crime rate emanating from America’s city cores, a crime rate that generates a prison population about 30 times higher than Germany.
You, have forgotten the most important about population in the USA. As long as congress in USA, refuses to stop supporting all the illegals with a life time government check. Population in the USA, will not decrease.