Will price of hydrogen fuel rise after 3 years when oil production slows down? Is hydrogen fuel cheap because it is a by-product of oil?

The answer is that we don't know what prices it will be at. It's too far in the future to tell. It will likely keep being a small, insignificant part of transportation and may fizzle out entirely in the next few decades due to the advances in battery electric technology that is likely the type of technology that will take over after the fall of oil. Therefore, hydrogen prices may not be affected by or have much importance after oil production slows down.

Hydrogen can be produced from fossil fuels. But it is not a common practice to make hydrogen from petroleum. Usually crude oil is separated into diesel, kerosene, gasoline, butane and propane, but not into hydrogen.

You seem to have all the answers, like what may happen in 3 years, so you tell us ..........

you need to go back to school and learn chemistry

Hydrogen comes from breaking down water into the 2 elements that make it --hydrogen and oxygen (H2O)

the technology is already available to produce hydrogen to drive an engine from a tank of water.Time to catch up on your science

Hydrogen is normally produced by steam reforming hydro carbons (from fossil fuels) there are other methods of manufacturing hydrogen but none are cheap

Hydrogen has to considered as an energy carrier, not as a fuel and as such it's usefulness is limited. except for liquid hydrogen-liquid oxygen rocket engines.