The Chicago Board Options Exchange, the biggest US options trading platform, agreed to pay a $6 million fine to settle charges it failed in its regulatory oversight, the Securities and Exchange Commission announced Tuesday. CBOE fell short of the requirements to prevent abusive short-selling, the SEC said. As such, the exchange failed to perform a core function of a self-regulatory organization. \"The proper regulation of the markets relies on SROs to aggressively police their member firms and enforce their rules as well as the securities laws,\" said Andrew Ceresneh, co-director of the SEC\'s division of enforcement. \"When SROs fail to regulate responsibly the conduct of their member firms as CBOE did here, we will not hesitate to bring an enforcement action.\" The CBOE case is the first levied against an exchange for violations related to regulatory oversight, the SEC said. Among the regulatory and compliance failures, CBOE failed to enforce a short-selling rule with a client because the company had not adequately train surveillance staff or ensure that investigators had read the rules, the SEC said. CBOE then took \"misguided and unprecedented\" steps of assisting that same client firm when it became the subject of an SEC investigation, the SEC said. CBOE, in a separate statement, said the exchange had implemented or was in the process of implementing all remedies identified by the SEC. \"This settlement marks a significant step in putting the SEC matter behind us, but our commitment to maintaining the very highest standards in regulation and compliance will be carried forward throughout the organization,\" it said.