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).
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?