Commitments and Contingent Liabilities Guaranteed Obligations Power s activities primarily involve the purchase and sale of energy and related products under transportation, physical, financial and forward contracts at fixed and variable prices. These transactions are with numerous counterparties and brokers that may require cash, cash-related instruments or guarantees. Power has unconditionally guaranteed payments to counterparties by its subsidiaries in commodity-related transactions in order to " support current exposure, interest and other costs on sums due and payable in the ordinary course of business, and " obtain credit. Under these agreements, guarantees cover lines of credit between entities and are often reciprocal in nature. The exposure between counterparties can move in either direction. In order for Power to incur a liability for the face value of the outstanding guarantees, its subsidiaries would have to " fully utilize the credit granted to them by every counterparty to whom Power has provided a guarantee, and " all of the related contracts would have to be  out-of-the-money  (if the contracts are terminated, Power would owe money to the counterparties). Power believes the probability of this result is unlikely. For this reason, Power believes that the current exposure at any point in time is a more meaningful representation of the potential liability under these guarantees. This current exposure consists of the net of accounts receivable and accounts payable and the forward value on open positions, less any collateral posted. Power is subject to " counterparty collateral calls related to commodity contracts, and " certain creditworthiness standards as guarantor under performance guarantees of its subsidiaries. Changes in commodity prices can have a material impact on collateral requirements under such contracts, which are posted and received primarily in the form of cash and letters of credit. Power also routinely enters into futures and options transactions for electricity and natural gas as pa