Shell and Phillips 66 are exploring a potential sale of their controlling stakes in the Explorer Pipeline, a transaction that could value the major U.S. energy infrastructure asset at roughly $3.5 billion, according to people familiar with the matter. The two energy giants hold a combined 61% ownership stake in the entity behind the refined products network. Energy Transfer and MPLX own the remaining 39% of the Explorer system. In operation since the early 1970s, the Explorer Pipeline stretches more than 1,800 miles. Alongside the Colonial Pipeline, Explorer is regarded as one of the most essential refined fuel arteries in North America.