CBOE's Automated Improvement Mechanism (AIM) is an automated process for crossing of any origin type, which provides potential for price improvement and a participation right through an auction process. By utilizing the AIM crossing mechanism, an order flow provider is afforded the opportunity to participate against their customers' orders (facilitation) or solicit another firm's liquidity (solicitation).

(NOTE: Available in all classes except SPX.)

See the table below for AIM rules for :

• AIM for Simple (non-complex) Orders
• AIM Customer to Customer Transactions
• AIM for Complex Orders
• AIM All Or None (AON) Solicitation - Simple and Complex

AIM for Simple (non-complex) Orders
Initiating Order and Contra Order must be entered as a pair.
Contra Order must be for full size of Initiating Order / can be facilitating or solicited.
Price must better NBBO if 49 contracts or less; 50 contracts or above can equal NBBO.
Auction period is 1 second; minimum improvement increment is .01. Contra Order guaranteed 40% if at best price (matched by multiple participants) or 50% (matched by one participant).
Entering Contra Order as a Market Order guarantees participation at best price (auto-matches best price of other auction participants).

AIM Cust-to-Cust (Simple Orders Only)
If both orders are Customer origin execution is immediate - no exposure to auction.
Cannot trade at same price as resting Customer order(s).
All else, same rules as above.

AIM For Complex Orders*
Complex orders having up to four legs and having a ratio of one-to-three or lower are eligible for the AIM mechanism.
Contra Order price must be at least .01 better than CBOE displayed market.
All else, same as AIM for Simple Orders.

AIM For Option: Stock Orders** (stock leg executes on CBSX)
Price must better NBBO by $.01 or $.02 if CBOE and CBSX are on the NBBO.
All else same as AIM for Simple Orders.
**Coming in early 2009: Ratios for stock:option orders (up to four legs, one leg stock)

AIM All Or None (AON) Solicitation - Simple and Complex
500 contract minimum.
Both orders must be AON.
Solicitation only (no Facilitated). If Contra Order is Firm, cannot be same give-up as Initiating Order.
Price must be at CBOE BBO (NBBO not required) but must improve resting Customer orders.
Contra Order can only be shut out if responses improve Contra Order price FOR FULL VOLUME.
All else same as AIM for Simple Orders..