If oil/gas prices were to stay unchanged, how much would a typical decline in price per year be because of depletion of the product???

The laws of supply and demand suggest that as the supply of oil declines, the price of oil will increase.

The price of oil is next to nothing.
supply and demand sees to puryfying transport storing and selling,of which the last three plus al the taxes at every stage make the biggest part of the total price.
But giving a stable price at the end user I would expect a higher price for the raw product where oil is concerned.
Gas mostly goes as is until it reaches the almost enduser.
But as a byproduct of oil I would also expect it to rise.