What's the route with the highest rebates on IBKR when selling FB Calls?

Can you tell me rich route pays the highest rebate, not sure if it was EMRD or PHLX? Thank you very much and good luck!

 

selling at $2.30, sold! $230 May 29

 

Well its not BATS, thank's IBKR for routing my order to the most expensive ECN of BATS. Commission was $30 to provide liquidity for 40 contracts of FB. Arg!

 

I usually get cheapest with EMRD on limit orders. I haven't been hardworking enough to check every exchange though.

 

Several extra round trips on 50 to 500 contracts adds up. If your getting rebates.