But the world economy will go into a depression that we have never seen on high oil prices, if they never lower the prices. It’s not sustainable.
Three errors here. 1st, what's not sustainable is an economy based on energy derived from oil. Change to an alternative, preferably sustainable, energy source.
2nd, the oilman is a capitalist entrepreneur doing exactly what the oilman is supposed to do by adjusting price according to supply/demand. Why blame the oilman? Capitalism is not based on any short term "good" for society, but on the long term theory that supply, demand, elasticity of demand, and alternatives will produce an end result that provides greater benefit to society than other price determining systems. This also assumes, or course, that all "costs" are built into the system and that the system operates freely between willing and knowledgeable sellers and buyers, each under no compulsion to sell or buy. And also, of course, none of this is actually true.
3rd, the local oilman should not be bad-mouthed because the scumbag, greedy, exploiting, polluting, defacing, corrupting oil industry controls the world. They have the "black gold," they and their parasitic speculators can set the price, you want it, so pay through your nose and like it. And if you don't like it, change the political system which allows this to happen.
IMO, in the long term "unsustainable" oil prices are good because finally the addicted US consumer might decide to get off her daily fix of cheap energy.