Oil prices are about 11 years low. To what extent can the situation affect economies of oil producing countries, especially Saudi Arabia and lran?

Saudi Arabia can survive because in long terms even if oil prices go below the current level, they will get the deficit from their foreign reserves. However, Iran cannot survive as it is not the case with them.

The biggest energy story in the world right now is the collapse of global oil prices. And for major producers like Russia or Iran or even Saudi Arabia, that's unsettling news.

How bad is it? One good place to start is with this excellent chart from The Economist looking at the "break-even" points for various countries. These are all nations that depend heavily on oil revenues for their national budgets — so when the price falls below the break-even point, the government starts running a deficit: