But why should oil producing countries suppose that the price of oil is only to get higher?

If a depression happens (and it could at any moment) in my opinion oil has no limits (downwards).

There are many parallels with 1929. Which I find most striking - the upper 1% of people in USA has something like half of all capital again after 1929.

It seems logical: elite needs happy herds only to accumulate wealth. once accumulating wealth on the shoulders of middle class is not possible anyomore, why would elites bother about middle class?

and you can't get that much anyomore, when you already have everything

The price of oil might fall soon. After all, we can only buy oil with money we borrow. If we can't borrow money, we can't buy oil, we stop importing oil, 12 million barrels a day of demand vanishes from the oil market, and Saudi Arabia, Iran, and Kuwait all stop exporting oil!

that sounds realistic..

Oh yeah, we're just going to stop importing oil and teach those Saudi bitches a thing or two!! I can see them shaking in their bathrobes now. from laughter.

The last times that the elites failed to take account of the middle classes, they ended up having to deal with people like these:

Arras, Robspierre, Danton , Marat, Lenin, Trotsky...

The world consumed more oil in 1939 than it did in 1929. A depression may cause consumption to decline a little, for a while, but it is not clear that it will cause consumption to decline faster than depletion. In addition, some of the oil that is being produced now is very expensive to produce. As prices go down, that production will come off line. A depression is also likely to increase political instability, further depressing production, if it does not lead to outright warfare.

Surely that indicates that to depress oil depletion then you would need a greater depression than the 30's, as supply and demand are going to be equal.
Counteracting that though somewhat is that AFAIK oil did not get more expensive in the 30's, and so there was less incentive to conserve.