Tallgrass Energy Partners has completed the purchase of its partner's stake in the Rockies Express Pipeline (REX).

The Leawood, Kan.-based company said May 9 it acquired Sempra U.S. Gas & Power's 25% membership interest in REX for $440 million in cash. Sempra U.S. Gas & Power is a unit of Sempra Energy (NYSE: SRE).

Tallgrass’ transaction brings with it about $640 million in debt, the portion of REX’s roughly $2.6 billion debt that Sempra holds.

REX is one of the largest pipelines ever constructed in the U.S., according to Tallgrass' website. The more than 1,700-mile pipeline stretches from northwestern Colorado and Wyoming to eastern Ohio. The long-haul design can support a capacity of 1.8 billion cubic feet per day.

Tallgrass entered the deal owning a 50% interest in REX, which it operates through subsidiary Rockies Express Holdings LLC. Sempra and Phillips 66 (NYSE: PSX) own the remaining interest in REX, 25% each.

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