Laclede will buy two of Southern Union Co.'s utilities, Missouri Gas Energy and New England Gas Co., for $1.02 billion.
Energy Transfer Equity's takeover of pipeline operator Southern Union Co closed early this year.
The deal announced Monday also includes the assumption of about $20 million in debt, so the companies value it at nearly $1.04 billion.
Laclede, a utility holding company, expects the deal to close next summer, and start to boost earnings a year after that.
The utilities had combined revenue of about $517 million in the 12 months ending in September. The deal will double Laclede's customer base to 1.2 million.
The Laclede Group Inc. is based in St. Louis. Southern Union is based in Houston.