The Diamondback pipeline ships diluent from BP Plc 430,000 bpd Whiting, Indiana, refinery through a junction in Gary, Indiana, to another pipeline in Illinois. The diluent is used in transporting heavy Canadian crude.

"The heavy oil crowd is long heavy oil, so diluents will still make sense," Zinsmeister told analysts and investors on the company’s second quarter earnings call. "We'll see growth over time … (but) we are looking at shipping opportunities of products other than diluent."

Any shift in products transported on the pipeline will not occur in 2019, he added.

The master limited partnership, formed by BP's U.S. pipeline unit, is also exploring financial options for a 2020 asset drop down from its sponsor BP Plc, but global trade tensions have made financing difficult, Zinsmeister said.

"We're ready to drop down some assets, market-conditions permitting," he said. "All options are on the table," he added, though he did not say which asset drop downs are most likely to occur.

(Reporting by Collin Eaton in Houston; Editing by Bernadette Baum and Marguerita Choy)