In this electronic era, after-market ticket sales seem to have moved from the asphalt expanse of the parking lot to the bright white lines of Craigslist.

While very few people offering tickets for sale were to be found yesterday at the U.S. Open's satellite parking lots at Pittsburgh Mills and Hartwood Acres, dozens of tickets were available yesterday online.

The United States Golf Association, which is running the U.S. Open, prohibits scalping -- defined as reselling tickets above their face value. Each Open ticket contains this wording:

"Resale or attempted resale of this ticket at a price higher than face value of this ticket is grounds for seizure or automatic cancellation of this license without refund or other compensation."

It doesn't forbid individuals from selling their tickets at or below face value, said spokesman Marty Parkes.

Open tickets, many priced below face value, are available on Craigslist and other Web sites like the eBay-owned StubHub.com.

One listing, posted on Craigslist yesterday at 4:12 p.m., even offered a free ticket to that afternoon's practice round.

"Tell me why I should give it to you versus someone else!" the listing said.

Other sellers said that they purchased the tickets months ago but had to change their plans.

"I ended up having to be in New York instead," said David Godmintz of San Francisco, who was selling his tickets at a discount on Craigslist.

Some sellers have been disappointed at the ticket prices. Charlie Walsh, a Shadyside resident and member of the PGA who was also selling on Craigslist, said, "I've done Craigslist for concerts in the past. Usually, I've found that you get a premium, but with the Open, it's really not the case."

But the anonymity of Craigslist and other online sites puts buyers at the risk of being defrauded, officials have warned.

"I have not heard of any online scams," said Mr. Parkes. As to whether golf fans ought to buy tickets online, Mr. Parkes said, "It's really an individual decision as to whether or not you trust the entity that you're buying from online."