Options on the E-mini S&P 500 Futures at the CME: what's the expiry date of the underlying future?

Question

The Chicago Mercantile Exchange (CME) has a variety of options on the E-mini S&P 500 (E1A,E2A,E3A,E4A,E5A,E1C,E2C,E3C,E4C,E5C,EW, EW1,EW2,EW3,EW4, and ES).

Looking at the contract specifications (e.g., EW (mirror)), the underlying is the E-mini S&P 500 Futures.

However, there exists more than one current listed contracts for the the E-mini S&P 500 Futures. Specifically, as mentioned on E-mini S&P 500 Futures Contract Specs (mirror), there are 5 listed for the the E-mini S&P 500 Futures (Five months in the March Quarterly Cycle (Mar, Jun, Sep, Dec)):

On which one are options on the E-mini S&P 500 Futures?

For example, if today (August 10, 2017) I purchase one call for EWQ7, does this mean that at 4:00 p.m. ET on the last business day of this month I have the right (let's ignore that contrarian instructions are forbidden for weekly & end-of-month options) to purchase the corresponding ESU6? or is it ESZ6?

Answer 1

I don't see EWQ6 in any of your links, so I can't say for certain, but when you buy an option contract on a future, the option will be for a specific future (and strike). So the page you're looking at may be for options on E-mini S&P 500 futures in general, and when you actually purchase one through your broker, you pick a specific expiry (which will be based on the "prompt" future, meaning the next future that expires after the option) and strike.

UPDATE:

Based on this page mirror, the option EWQ7 is an option on the ESU7 (SEP 2017) future. The next 3 monthly options use ESZ7 as the underlier, which confirms that they use the next prompt future as the underlier.