Exhibit 99.1 NEWS - ------------------------------------------------------------------------------- KeySpan Corporation For Immediate Release Contacts: Investors Media Relations George Laskaris Andrea Staub 718.403.2526 516.545.5052 516.824.1241 (pager) KeySpan Completes Exchange With Houston Exploration Exchange Valued at $449 Million Reduces Ownership Interest to 24% New York, June 2, 2004 - KeySpan today announced the successful completion of an exchange transaction with The Houston Exploration Company (NYSE: THX) valued at $449 million, which reduced KeySpan's ownership of Houston Exploration from approximately 55% to 24%. Under the terms of the transaction, KeySpan exchanged 10.8 million shares of Houston Exploration common stock for all the stock of Seneca-Upshur Petroleum, Inc., a wholly owned subsidiary of Houston Exploration. Houston Exploration retired 4.6 million shares and issued 6.2 million shares in a public offering. Based on the Houston Exploration announced offering price of $48.00 per share, KeySpan's Seneca-Upshur's shares were valued at the equivalent of $449 million, or $41.57 per share. Seneca-Upshur's assets consist of Appalachian producing properties valued at $60.0 million dollars, and $389.0 million in cash. Seneca-Upshur's proven reserves of 50.5 billion cubic feet of natural gas equivalent (Bcfe) represent approximately 7% of Houston Exploration's proved reserves. - -------------------------------------------------------------------------------- A member of the Standard & Poor's 500 Index, KeySpan Corporation (NYSE:KSE) is the fifth largest distributor of natural gas in the United States and the largest in the Northeast, operating regulated gas utilities in New York, Massachusetts and New Hampshire, serving 2.5 million customers. These customer-focused businesses are complemented by a portfolio of service companies which offer energy-related products, services and solutions to homes and businesses. KeySpan is also the largest electric generator in New York State. We own approximately 6,600 megawatts of generating capacity, providing power to 1.1 million customers of the Long Island Power Authority on Long Island and supplying approximately 25 percent of New York City's capacity needs. In addition to these assets, KeySpan has strategic investments in natural gas exploration, production, pipeline transportation, distribution and storage, and Canadian gas processing. KeySpan has headquarters in Brooklyn, New England and Long Island. For more information, visit KeySpan's web site at www.keyspanenergy.com. Certain statements contained herein are forward-looking statements, which reflect numerous assumptions and estimates and involve a number of risks and uncertainties. For these statements, we claim the protection of the safe harbor for forward-looking statements provided by the Private Securities Litigation Reform Act of 1995. There are possible developments that could cause our actual results to differ materially from those forecast or implied in the forward-looking statements. You are cautioned not to place undue reliance on these forward-looking statements, which are current only as of the date of this filing. We disclaim any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. Among the factors that could cause actual results to differ materially are: general economic conditions, especially in the Northeast United States; available sources and costs of fuel; volatility of energy prices in a deregulated market environment as well as in the source of natural gas and fuel used to generate electricity; potential write-down of our investment in natural gas properties when natural gas prices are depressed or if we have significant downward revisions in our estimated proved gas reserves; federal and state regulatory initiatives that increase competition, threaten cost and investment recovery and impact rate structure; our ability to successfully reduce our cost structures; implementation of new accounting standards; the degree to which we develop unregulated business ventures, as well as federal and state regulatory policies affecting our ability to retain and operate those business ventures; our ability to identify and make complementary acquisitions, as well as the successful integration of those acquisitions; inflationary trends and interest rates; and risks detailed from time to time in reports and other documents filed by us with the Securities and Exchange Commission. 2