How have falling oil prices affected the finances of Saudi Arabia?

How have falling oil prices affected the finances of Saudi Arabia? Captain Capitalism writes,

First we have economic growth. This is NOT GDP, though the graph will look that way. It is YEAR OVER YEAR economic growth, ie- GDP growth. In 2011 and 2012 Saudi Arabia's economy was booming, logging a near one third growth rate for both years. Not 1/3%. 33%. Growth collapsed quickly in 2013 and 2014, entering a NEGATIVE 13% GDP for 2015. Of course, Western nations aren't accustomed to such volatility in their growth rates, but it still doesn't change the fact 2015 was a devastating year for Saudi Arabia.

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