UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C.  20549

FORM 8-K

CURRENT REPORT

Pursuant To Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported)                       December 19, 2006

TC PipeLines, LP

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code                       (508) 871-7046

Not Applicable

(Former name or former address if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

o  Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o  Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o  Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 2.01. Completion of an Acquisition or Disposition of Assets.

On December 19, 2006, TC Tuscarora Intermediate Limited Partnership, a wholly-owned subsidiary of the Partnership, completed the acquisition of an additional 49% general partnership interest in Tuscarora Gas Transmission Company (“TGTC”) for approximately $99.6 million, with Tuscarora Gas Pipeline Company (“TGPC”), a wholly-owned subsidiary of Sierra Pacific Resources.  The Partnership funded the purchase price with a loan under the credit facility that it entered into on December 12, 2006 with SunTrust Bank and other lenders.  The Partnership also indirectly assumed approximately $37 million of debt of TGTC. This acquisition increased the Partnership’s interest in TGTC to 98% from 49%. TransCanada Corporation (“TransCanada”), the parent company of TC PipeLines GP, Inc. and the sole general partner of the Partnership, indirectly holds a 1% ownership interest in TGTC. Pursuant to an agreement (the “Option Agreement”), for approximately one year after December 19, 2006, the Partnership will have an option to purchase the remaining 1% interest in TGTC from TGPC for $2 million, subject to certain closing adjustments.

The Partnership’s purchase agreement for the additional 49% general partnership interest and the Option Agreement were attached as exhibits to the Partnership’s November 1, 2006 Form 8-K.

Item 9.01.  Financial Statements and Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Exhibit 99.1

News Release

TC PipeLines, LP acquires Tuscarora Gas Transmission Company

Calgary, Alberta — December 19, 2006 — (Nasdaq: TCLP) — TC PipeLines, LP (the Partnership) today announced it has closed its acquisition of Sierra Pacific Resources’ 50 per cent interest in Tuscarora Gas Transmission Company (Tuscarora) for approximately US$100 million. The Partnership has also indirectly assumed US$37 million of Tuscarora debt. TC PipeLines, LP now owns or controls 99 per cent of Tuscarora. TransCanada Corporation (TransCanada), the parent company of the Partnership’s general partner, TC PipeLines GP, Inc., indirectly holds a 1 per cent ownership interest.

“Tuscarora is a high quality asset with a strong long-term contract profile, rate stability and a history of steady organic growth,” said Russ Girling, president and chief executive officer of TC PipeLines GP, Inc., general partner of TC PipeLines, LP. “These attributes, combined with the Partnership’s existing ownership of Tuscarora and the pipeline’s physical connection to TransCanada’s system, make Tuscarora an excellent investment for TC PipeLines LP, and our unit holders.”

The Partnership also announced the closing of a US$410 million senior credit facility. Borrowings under the credit facility will bear interest based, at the Partnership’s election, on the London interbank offered rate (LIBOR) or the prime rate plus, in either case, an applicable margin. The effective interest rate as at the closing of the credit facility on December 12, 2006 was 6.07 per cent. This represents a decrease in the interest rate from the previous rate of 6.325 per cent. The facility was used to refinance an existing bridge facility and to finance the acquisition of the additional ownership interest in Tuscarora. The Partnership has the right to make optional repayments on the facility. The facility has a five-year term subject to two one-year extensions.

Tuscarora owns a 240-mile, 20-inch diameter, United States interstate pipeline system with a subscribed capacity of approximately 180 MMcf/d. The Tuscarora pipeline system originates at an interconnection point with existing facilities of TransCanada’s Gas Transmission Northwest System near Malin, Oregon and runs southeast through northeastern California and northwestern Nevada, terminating near Wadsworth, Nevada.

Tuscarora has firm transportation contracts for over 95 per cent of its available contracted capacity. A subsidiary of Sierra Pacific Resources holds contracts representing 69 per cent of the total available capacity, the majority of which expires on October 31, 2017.

A TransCanada subsidiary will become the operator of Tuscarora, which is currently operated by an affiliate of Sierra Pacific Resources. TransCanada has provided gas control services for the Tuscarora pipeline system since late 2002.

The Tuscarora acquisition follows the Partnership’s acquisition in April 2006 of an additional 20 per cent of Northern Border Pipeline Company, an interstate pipeline that transports natural gas from the Montana-Saskatchewan border to markets in the U.S. midwest. Northern Border Pipeline is a leading transporter of natural gas imported from Canada into the U.S.

TC PipeLines, LP is a publicly traded limited partnership. It owns a 50 per cent interest in Northern Border Pipeline Company, a Texas general partnership, and a 99 per cent interest in Tuscarora Gas Transmission Company, a Nevada general partnership. Northern Border Pipeline owns a 1,249-mile United States interstate pipeline system that transports natural gas from the Montana-Saskatchewan border to markets in the midwestern United States. Tuscarora owns a 240-mile United States interstate pipeline system that transports natural gas from Oregon where it interconnects to TransCanada’s Gas Transmission Northwest System. TC PipeLines, LP is managed by its general partner, TC PipeLines GP, Inc., an indirect wholly owned subsidiary of TransCanada Corporation. TC PipeLines GP, Inc., also holds common units of the Partnership. Common units of TC PipeLines, LP are quoted on the NASDAQ Stock Market and trade under the symbol “TCLP.”

Cautionary Statement Regarding Forward-Looking Information

This news release may include forward-looking statements regarding future events and the future financial performance of TC PipeLines, LP. Words such as “believes,” “expects,” “intends,” “forecasts,” “projects,” and similar expressions identify forward-looking statements. All forward-looking statements are based on the Partnership’s current beliefs as well as assumptions made by and information currently available to the Partnership. These statements reflect the Partnership’s current views with respect to future events. The Partnership assumes no obligation to update any such forward-looking statement to reflect events or circumstances occurring after the date hereof. Important factors that could cause actual results to materially differ from the Partnership’s current expectations include regulatory decisions, particularly those of the Federal Energy Regulatory Commission and the Securities and Exchange Commission, the ability of Northern Border Pipeline to recontract its available capacity at maximum rates, operational decisions of Northern Border Pipeline’s operator, the failure of a shipper on either one of the Partnership’s pipelines to perform its contractual obligations, cost of acquisitions, future demand for natural gas, overcapacity in the industry, and other risks inherent in the transportation of natural gas as discussed in the Partnership’s filings with the Securities and Exchange Commission, including the Partnership’s Annual Report on Form 10-K for the year ended December 31, 2005.

— 30 —