Williams Cos. is in advanced talks to acquire Momentum Midstream, a natural gas pipeline operator, for about $5.5 billion, according to people familiar with the matter. Both reports describe the proposed price as approximately $5.5 billion and characterize the discussions as advanced but not yet final. The deal, if completed, would be among the largest acquisitions by Williams, the sources say. The reports do not provide additional terms, financing details, or timing for a potential announcement or closing. They also do not specify whether regulators or customary approvals would be required, nor do they outline any expected synergies or strategic rationale beyond the acquisition itself. For now, the information is limited to the existence of advanced negotiations and the approximate valuation referenced by sources. Williams and Momentum Midstream are not quoted in the provided summaries.