RALEIGH, N.C. (AP) — The heads of Duke Energy Corp. and Piedmont Natural Gas Co. are on the witness stand as they explain why North Carolina regulators should approve their merger.

The state Utilities Commission on Monday hears Duke Energy CEO Lynn Good and Piedmont Natural Gas head Thomas Skains defend their plan. Duke Energy plans to buy its fellow Charlotte-based company for about $5 billion.

The companies were already working together to build a pipeline to deliver natural gas from West Virginia to North Carolina when Duke announced its planned purchase last fall.

Duke’s move comes as power companies are increasingly switching from burning coal to natural gas to generate electricity and buy suppliers to control costs.

Piedmont has customers across most of North Carolina; around Nashville, Tennessee; and around Spartanburg, South Carolina.