6. TRANSACTIONS WITH AFFILIATES
We are a participant in WPZ's cash management program, and we make advances to and receive advances from WPZ. At June 30, 2012 and December 31, 2011, the advances due to us by WPZ totaled approximately $61.5 million and $52.0 million, respectively. These advances are represented by demand notes. The interest rate on these intercompany demand notes is based upon the daily overnight investment rate paid on WPZ's excess cash at the end of each month, which was approximately 0.01 percent at June 30, 2012. The interest income from these advances was minimal during the six months ended June 30, 2012 and June 30, 2011. Such interest income is included in “Other Income – net: Interest income – Affiliated” on the accompanying Statement of Comprehensive Income.
The Williams Companies, Inc. (Williams) charges its subsidiary companies for management services provided by it and other affiliated companies. Such corporate expenses charged by Williams, WPZ, and other affiliated companies, for the six months ended June 30, 2012 and 2011, were $21.3 million and $18.0 million, respectively. These expenses are included in “General and administrative expense” on the accompanying Statement of Comprehensive Income. Management considers the cost of these services to be reasonable.
We have no employees. Services are provided to us by an affiliate, Northwest Pipeline Services LLC (NPS). Pursuant to an administrative services agreement, NPS provides personnel, facilities, goods, and equipment not otherwise provided by us that are necessary to operate our business. In return, we reimburse NPS for all direct and indirect expenses it incurs or payments it makes (including salary, bonus, incentive compensation, pension and other benefits) in connection with these services. For the six months ended June 30, 2012 and 2011, we were billed $33.7 million and $30.9 million, respectively. Such expenses are primarily included in “General and administrative” and “Operation and maintenance” expenses on the accompanying Statement of Comprehensive Income.
During the periods presented, our revenues include transportation transactions and rental of communication facilities with subsidiaries of Williams. Combined revenues for these activities, for the six months ended June 30, 2012 were minimal. Combined revenues for the six months ended 2011 were $12.1 million. The reduction in revenues from 2011 is a result of Williams' spin-off of its former exploration and production business, which was completed on December 31, 2011. These revenues, associated with transportation transactions, are now reflected with the revenues from outside parties.
During the six months ended June 30, 2012 and 2011, we declared and paid equity distributions to our parent of $73.0 million and $64.0 million, respectively. During July 2012, we declared and paid equity distributions of $34.5 million to our parent.
During the six months ended June 30, 2012 and 2011, we received contributions of $2.3 million and $3.5 million, respectively, from our parent to fund a portion of our expansion related expenditures for additions to property, plant, and equipment. In July 2012, our parent authorized an additional $1.2 million capital contribution to us to fund a portion of our expenditures for additions to property, plant and equipment.
We have entered into various other transactions with certain related parties, the amounts of which were not significant. These transactions and the above-described transactions are made on the basis of commercial relationships and prevailing market prices or general industry practices.