Exhibit 21

SIGNIFICANT SUBSIDIARIES OF CENTERPOINT ENERGY, INC.

The following subsidiaries are deemed “significant subsidiaries” pursuant to Item 601(b) (21) of Regulation S-K:

Utility Holding, LLC, a Delaware limited liability company and a direct wholly owned subsidiary of CenterPoint Energy, Inc.

CenterPoint Energy Investment Management, Inc., a Delaware corporation and an indirect wholly owned subsidiary of CenterPoint Energy, Inc.

CenterPoint Energy Resources Corp., a Delaware corporation and an indirect wholly owned subsidiary of CenterPoint Energy, Inc.

CenterPoint Energy Houston Electric, LLC, a Texas limited liability company and an indirect wholly owned subsidiary of CenterPoint Energy, Inc.

CenterPoint Energy Services, Inc., a Delaware corporation and an indirect wholly owned subsidiary of CenterPoint Energy, Inc.

Enable Midstream Partners, LP (Enable), a Delaware limited partnership. CenterPoint Energy, Inc. indirectly owns 58.3% of the limited partner interests.

Subsidiaries of Enable:

Subsidiary            State of Incorporation/Organization

Enable Intrastate Holdings II, LLC        Delaware

Enable Oklahoma Intrastate Transmission, LLC     Delaware

Enable Gathering & Processing, LLC     Oklahoma

Enable Gas Gathering, LLC     Oklahoma

Enable Products, LLC     Oklahoma

Enable Gas Transmission, LLC     Delaware

Waskom Gas Processing Company     Texas

Enable Prism Holdings, LLC     Delaware

(1) Pursuant to Item 601(b) (21) of Regulation S-K, registrant has omitted the names of subsidiaries, which considered in the aggregate as a single subsidiary, would not constitute a “significant subsidiary” (as defined under Rule 1-02(w) of Regulation S-X) as of December 31, 2013.