Oil prices have gotten crushed for the last six months. The extent to which that was caused by an excess of supply or by a slowdown in demand has big implications for where prices will head next. People wishing for a big rebound may not want to read farther.

Goldman Sachs released an intriguing analysis on Wednesday that shows what many already suspected: The big culprit in the oil crash has been an abundance of oil flooding the market. A massive supply shock in the second half of last year accounted for most of the decline. In December and January, slowing demand contributed to the continued sell-off. Goldman was able to quantify these effects.

The Culprit Is in Blue

Goldman’s model is simple on its face, looking at just two variables over time: the price of oil and the value of U.S. stocks (as measured by the S&P 500). The idea is that the stock market is a pretty good indicator of economic demand. So when stocks move in tandem with oil prices, demand is in the driver’s seat. When the price of oil moves in the opposite direction of stocks, the shock is coming from supply.

It’s a bit more complicated than that—for the statistically inclined, Goldman uses a “vector autoregression with sign restrictions”—but you get the idea. In the following chart, they split apart the effects of demand shocks (left) from supply shocks (right).

Demand & Supply

The chart on the left shows what you might expect: strong demand leading up to a precipitous decline during the recession beginning in late 2008. The supply chart on the right shows a shock of undersupply in late 2007, leading to years of relatively steady supply expectations. Oversupply shocks picked up, beginning in 2012, as U.S. shale-oil production exceeded expectations, culminating in a piercing shock of oversupply last year that sent markets reeling.

The big take-away: “[T]he decline in oil has been driven by an oversupplied global oil market,” wrote Goldman economist Sven Jari Stehn. As a result, “the new equilibrium price of oil will likely be much lower than over the past decade.”

Source-Bloomberg