The particular regulation which determines the minimum amount of margin collateral that each broker is required to collect from clients transacting in U.S. exchange listed products generally depends upon the following 3 factors:

1. Product Classification - the principal determinant of regulatory oversight is based upon whether the product is classified as a security or commodity. Security products, including stocks, bonds, options and mutual funds are regulated by the Securities and Exchange Commission (SEC).  Commodity products, which include futures contracts and options on futures contracts, are regulated by the Commodities Futures Trading Commission (CFTC).  Single stock futures, a special class of futures contracts, are considered a hybrid product subject to joint regulation by the SEC and CFTC.

In the case of security products, the US central bank referred to as the Federal Reserve (FRB) holds responsibility for regulating the extension of credit by brokers and dealers.  This is accomplished through Regulation T, or Reg T as it is commonly referred, which provides for establishment of a margin account and which imposes the initial margin requirement and payment rules on certain securities transactions.  For example, on stock purchases, Reg T currently requires an initial margin deposit by the client equal to of 50% of the purchase value, allowing the broker to extend credit or finance the remaining 50%.  Reg T does not establish margin requirements for securities options which fall under the jurisdiction of exchange rules (subject to SEC approval).  In addition, the FRB has excluded from Reg T the authority to establish either initial or maintenance margin requirements on securities positions held in a portfolio margining account.  here margin authority resides with the security exchanges whose rules are subject to SEC approval. 

The authority for establishing margin rates on commodity products resides with the listing exchanges, with the exception of broad based stock index futures, for which the FRB has delegated authority to the CFTC.

In the case of single stock futures, margin is set by the listing exchange and subject to SEC approval to the extent the position is carried in a securities account, and subject to an agreement that the margin be equivalent whether held in a securities or commodities account.  Margin for single stock futures are currently set at 20% of the underlying stock value.

2. Initial or Maintenance - initial margin generally refers to the amount of money or its equivalent that the customer must deposit in order to initiate the position and maintenance margin the amount of equity which must be maintained in order to continue holding the position. As noted above, Reg T controls the initial margin requirement on securities transactions.  The rules of the listing exchanges specify the maintenance margin requirements on security transactions subject to SEC approval.  The maintenance margin requirement for long stock positions is currently set at 25% although brokers often establish 'house margin' requirements in excess of that, particularly where the security is considered low-priced or subject to volatile price changes.

Commodities exchanges establish both the initial and maintenance margin requirements for products which they list (subject to provisions for broad based index futures and single stock futures as noted above).

3. Listing Exchange - as noted above, in the case of US securities products the listing exchange has the authority to establish rules for the maintenance margin requirement on positions held in a Reg T margin account and initial and maintenance margin (currently the same) for positions held in a portfolio margin account. Exchange margin rules, however, require prior SEC approval which acts to ensure that margin requirements are set  in a consistent manner across exchanges.  

Subject to the provisions noted above, commodities exchanges maintain authority to establish both initial and maintenance margin requirements.  As a general rule, US commodities exchanges employ the same risk-based margining methodology referred to as SPAN for determining the margin requirement on listed positions with each exchange specifying the relevant SPAN input factors (e.g., Price Scan Range, Volatility Scan Range, Spread Charges, Combined Commodity offsets).