PHILADELPHIA — A Pennsylvania appeals court appeared skeptical of gas drilling rules that would limit what “trade secrets” the industry must share after a spill.

The Commonwealth Court also heard arguments Wednesday on whether doctors treating an ill patient should have to keep information disclosed to them confidential.

Pennsylvania is trying to update 20-year-old laws to oversee the drilling boom in the Marcellus Shale. But the state’s high court last year threw out much of the industry-friendly regulations passed in 2012, which would have limited local oversight of drilling operations.

In Commonwealth Court arguments Wednesday, President Judge Dan Pellegrini asked whether drilling companies alone should know what chemicals are “in the secret sauce” used in the hydraulic fracturing, or fracking, process. Millions of gallons of fluids are forced into the earth in fracking to break through the shale.

Under the existing law, companies must disclose the chemicals involved, but can make exceptions for what they deem trade secrets.

“That kind of takes your breath away,” Pellegrini said.

On another point, the court was asked to order that contamination notices cover private water sources along with public water supplies. About 3 million people in Pennsylvania get their water from private sources, lawyer John Smith argued on behalf of several communities fighting provisions of the 2012 law, known as Act 13.

Industry lawyer David Overstreet challenged the public criticism of his clients, who pay more than $200 million a year in impact fees to affected communities, state agencies and others in Pennsylvania.

“People are under the impression that we’re out to rape and pillage,” said Overstreet, who represents the Pennsylvania Independent Oil and Gas Association and other trade groups. “This is an industry that’s benefiting tens of thousands of people.”

The drilling industry flocked to Pennsylvania in 2008 to tap into the Marcellus Shale, the nation’s largest-known natural gas formation.

The court did not immediately indicate when it would rule.