Sunoco Logistics Partners L.L.P. disclosed Thursday it is planning to build an additional pipeline to deliver Marcellus Shale products to Marcus Hook, reflecting a growing market for liquid fuels derived from the region's shale drilling.

The Philadelphia company said it now intends to build two pipelines simultaneously, as part of its Mariner East 2 project. The Mariner East 2 project, announced in November, is the second phase of a plan to move materials like propane, butane and ethane from Appalchian shale-gas fields to the Marcus Hook Industrial Complex southwest of Philadelphia.

The new twin pipelines would largely follow the route of its first Mariner East project, an 84-year-old repurposed fuel pipeline crossing Pennsylvania that went into service in December.

Sunoco Logisitics has been acquiring rights of way for the new 350-mile corridor that provide for construction of two new pipes. Landowners told the company that they preferred both pipelines to be installed together to minimize disturbances, Sunoco spokesman Jeffrey Shields said.

Shields said that by building both pipelines simultaneously also "also makes business sense" because it would reduce construction costs.

The second new pipeline is still tentative. Sunoco Logisitics needs to hold an "open season" to solicit customers to commit to shipping their products before committing to the expanded project.

"We can't say it's a done deal," Shields said.

Sunoco Logistics' expanding ambitions for the Mariner East project reflect a bullish outlook on production from the Marcellus Shale formation in Western Pennsylvania and the Utica Shale formation in Ohio and West Virginia.

Both formations produce what is known as "wet gas," which includes substantial amounts of high-value liquids like ethane, propane and butane. Those materials are coveted by the petrochemical industry as building blocks in the production of plastics and other complex compounds.

Having separate pipelines would give the company additional flexibility to deliver different products simultaneously, Shields said.

State officials and industry supporters say the pipelines create promising economic development possibilities; they are already fueling a major industrial expansion in Marcus Hook. But opposition has emerged from residents near the pipelines, who have joined with environmental activists who see the pipelines as a boost to additional gas drilling and dependence upon fossil fuels.