The Williams Cos. Inc. announced an unsolicited takeover bid of about $4.9 billion Thursday for pipeline company Southern Union Co., which agreed last week to a sale to Energy Transfer Equity LP.

Williams, which also operates gas pipelines, said it would offer $39 per share in cash and top Energy Transfer's bid of $33 per share, or $4.2 billion.

The announcement came after the markets closed and sent Southern Union shares higher after hours.

Southern Union rose 34 cents to $34.15 in regular trading, then jumped $5, or 14.6 percent, to $39.19 in about a half-hour of late trading. Williams shares closed at $29.23, down 9 cents, and fell another 89 cents, or 3 percent, to $28.34 in late trading.

Williams said Southern Union would complement its own business, create a network of nearly 30,000 miles of regulated pipelines and save $50 million a year for the combined companies.