Ethane prices slumped for the third straight week, pulling this week’s price of the hypothetical NGL barrel to a 10-week low at Mont Belvieu, Texas, and a 13-week low at Conway, Kan.

The Mont Belvieu ethane price is down 20.5% from its high in late June, while Conway’s price has endured a 31.4% hit since its peak in early June. Margins crashed 61% at Mont Belvieu and 49.2% at Conway in the past week.

Only rising prices for isobutane and C5+ at Mont Belvieu allowed NGL to avoid another rout like last week’s, when the Texas barrel fell 6.7% and Kansas took a 7.8% hit.

Behind these summer doldrums are the basics of supply and demand. With plenty of supply and not enough demand yet, NGL prices ride the waves of the global crude oil markets.

On June 23, West Texas Intermediate (WTI) peaked for the year, closing at $50.11 per barrel. By July 20, WTI was down 10.3%. That’s the ceiling.

Frac spread chart for July 22. The floor is set by the price of natural gas, typically the benchmark Henry Hub price. From its peak of $2.94 per million Btu on June 29, it had shed 7.5% of its value by July 20.

And the near-term outlook is “not too good,” as depicted by energy consultancy Douglas-Westwood. The firm sees offshore projects coming to fruition in the next year as adding 1.8 million barrels per day (MMbbl/d) of crude to a market drenched with supply.

If it appears the ceiling is caving in, the floor is giving out, too.

“Beyond oil, gas is growing at twice the rate of oil in terms of production growth,” said Steve Robertson, a director for Douglas-Westwood, during the firm’s recent webcast. “We need to get through this wave of additional oil supply that’s come through levels of investment we saw prior to the downturn, and that really won’t kick in until 2018 onwards.”

Ready for some cheer? Who isn’t? First, note the Reuters item on MidstreamBusiness.com with “pain” in the headline:

“The unusually large amount of gasoline and oil in storage, combined with expectations of a ramp-up in crude production, has made traders more bearish on the price outlook for late 2016 and early 2017.”

That’s the market outlook, which is based on a predicted trajectory of supply and demand. Geopolitics, however, brings its own brand of volatility.

NGL prices for July 22. Noting the horrific terror attack in Nice, France, followed by the failed coup in NATO member Turkey, Stratas Advisors adjusted its view and now considers geopolitics to be neutral factor to positive factor in the price of oil.

“The coup attempt has created additional uncertainty about the supply of crude with concerns about possible interruption of crude flows through the Bosporus and the Dardanelles,” Stratas said. The analysts believe the coup attempt may signal the start of a period of instability for Turkey.

The U.S. Energy Information Administration’s (EIA) weekly natural gas storage report for the week ending July 15 came up shy of the Bloomberg consensus expectation that 40 billion cubic feet (Bcf) would be added. The EIA reported the addition of 34 Bcf for a total of 3.277 trillion cubic feet (Tcf).

That total is 16.8% above the total last year at the same time of 2.806 Tcf and 20.6% over the five-year average of 2.718 Tcf.

Joseph Markman can be reached at jmarkman@hartenergy.com and @JHMarkman.

Resin prices for July 22.