March 20 - Standard & Poor's Ratings Services today assigned its 'A-' rating to Colonial Gas Co.'s $25 million 3.296% senior notes, series A, due March 15, 2022, and its $25 million 4.628% senior notes, series B, due March 15, 2042. The ratings on Colonial Gas (A-/Stable/--) are based on the consolidated credit profile of its ultimate parent, U.K.-based National Grid PLC (NG PLC). Colonial Gas is a gas distribution company serving about 194,000 customers in northwest Boston and in Cape Cod. The company is a wholly owned subsidiary of KeySpan Corp., which is in turn a subsidiary of U.S.-based utility holding company National Grid USA, a wholly owned subsidiary of NG PLC.. National Grid USA is also a subsidiary of intermediate holding company National Grid Holdings Inc. The ratings on NG PLC and its subsidiaries reflect our view of the strong and predictable cash flows from the group's low-operating-risk electricity and gas network operations in the U.K. and the U.S.; regulatory regimes in each of those countries that we consider to be broadly supportive of credit quality; a consistently applied strategic and financial policy; and a proven track record of managing large acquisitions. These strengths are offset by NG PLC's relatively high financial leverage; a substantial capital expenditure program and unchanged dividend policy that together will likely result in negative free cash flows over the medium term; regulatory reset risk in the U.S. and the U.K.; and exposure to foreign exchange risks and inflation, which add volatility to Standard & Poor's-adjusted credit measures. RELATED CRITERIA AND RESEARCH -- Liquidity Descriptors For Global Corporate Issuers, Sept. 28, 2011 -- Principles Of Credit Ratings, Feb. 16, 2011 -- Use Of CreditWatch And Outlooks, Sept. 14, 2009 -- Business Risk/Financial Risk Matrix Expanded, May 27, 2009 -- Analytical Methodology, April 15, 2008 -- Assessing U.S. Utility Regulatory Environments, Nov. 7, 2007 RATINGS LIST Colonial Gas Co. Corporate Credit Rating A-/Stable/-- New Rating Colonial Gas Co. Senior Unsecured $25 Mil. 3.296% Senior Notes, Ser A, Due March 15, 2022 A- $25 Mil. 4.628% Senior Notes, Ser B, Due March 15, 2042 A- Complete ratings information is available to subscribers of RatingsDirect on the Global Credit Portal at www.globalcreditportal.com. All ratings affected by this rating action can be found on Standard & Poor's public Web site at www.standardandpoors.com. Use the Ratings search box located in the left column.