Low oil-and-gas prices are poised to shake up yet another part of the nation’s energy economy, spurring a merger battle among companies that own the key pipelines that move fuels around the country. Williams WMB 25.90 % Cos., a large natural-gas pipeline operator, said it hired bankers and lawyers to help it review strategic alternatives, including a sale, after rejecting a roughly $48 billion unsolicited takeover that would have been the largest energy deal in the U.S. this year. Shares in the Tulsa, Okla., company soared to an all-time high of $60.86, up 26%, giving the more than 100-year-old company a market valuation of $45.58 billion. Shares of its would-be buyer fell nearly 5% to $65.06. Cheap energy has stronger companies across the industry—including exploration and drilling companies—eyeing weaker rivals. But deals have been few as buyout candidates hold out for richer offers. Dallas-based pipeline company Energy Transfer Equity […]