VALLEJO, Calif. -- A Pacific Gas & Electric Co. spokesman said Thursday morning that the utility has received hundreds of calls about a "rotten egg" smell detected in natural gas supplied to homes and businesses from the Oregon border to the Bay Area.

PG&E spokesman David Eisenhauer said the smell is the result of too much odorant being added to the gas.

He said the odorant, mercaptan, is used to detect leaks and was added to a gas transmission line in Malin, Ore. PG&E is still trying to determine the specific site where the mercaptan was added, he said.

The smell should dissipate by this afternoon and be completely out of the gas transmission line system by 2 a.m. Friday, Eisenhauer said.

The extra mercaptan in the transmission line was first detected at about midnight Wednesday at the Burney compression station in Shasta County, Eisenhauer said. The first complaints about the smell came from the Redding-Red Bluff area.

The smell has since been reported in Solano, Sonoma and Napa counties and parts of the East Bay, Eisenhauer said.

"We've gotten hundreds of calls, more than 600," Eisenhauer said.

The mercaptan is harmless but PG&E customers who are concerned about it can call the PG&E safety hotline at (800) 743-5000, Eisenhauer said.

The natural gas from Canada flows to the Bay Area through a pipeline from the Oregon border to the East Bay, where it connects to another pipeline that comes up from the southern part of the state. The pipes vary from 36 to 42 inches in diameter, Eisenhauer said.

The rotten egg smell will be further diluted at the connection point, and PG&E customers in the East Bay and points south should experience a much less powerful smell than customers farther north, Eisenhauer said.