The two Capline owners with US Midwest refining operations want to ensure they do not lose an important crude source as they and another partner evaluate reversing the oil pipeline, the nation’s largest, executives with operator Marathon Petroleum Corp said in an interview.

Don Templin, Marathon’s executive vice president of supply, transportation and marketing, said after the company’s quarterly earnings call that Marathon maintains many crude-sourcing options to ensure access to the best-priced oil of the day.

He said Capline’s refining partners – Marathon and BP - want to evaluate all such options “and make sure they’re comfortable that a reversal doesn’t impact them in a negative way.”

The third and majority Capline owner, Plains All American Pipeline, has repeatedly expressed support for reversing the 1.2 million barrels per day (mbpd) pipeline, which once moved high volumes of imports and Gulf of Mexico crude into the Midwest.

Now the region is well supplied by domestic shale oil, siphoning Capline’s relevance in the region. Plains’ 600,000 bpd portion of the line averaged 152,000 bpd in flows last year, according to a regulatory filing.

Marathon has been more circumspect, and BP declined comment. Marathon has said another south-to-north option would be needed if Capline is reversed, while noting it could move Canadian and North Dakota Bakken crude south to Louisiana refineries. Chief financial officer Tim Griffith said in the interview that reversal talks also are addressing how to feed Capline in Illinois with sufficient and economical north-to-south flows.