USGA officials have said they were working hard to make sure pin placements on Oakmont's slick, sloping greens were tough but fair for the 156-man field at the US Open.

Some players said scores could soar depending on the course set-up.

"I just think that we're going to all see what happens, because they can go crazy on pin locations and make it impossible," world number one Tiger Woods told reporters.  "But if they put pins in generous spots, I think it will be just a fantastic test."

The US Golf Association, criticized in the past for pushing courses to the edge in difficulty, said it was striving to find the right balance.

"These greens are scary. They are fast, make no mistake about it," Jim Hyler, chairman of the USGA championship committee, told reporters.  "They are indeed a true test of putting skill and nerves, and they really place a premium on approach shots."

Hyler said crews have been scrutinizing 90 different pin placements on the greens every day since last Friday, including positions for a possible 18-hole playoff on Monday.

"We are looking at every one of them every day to make sure that we are giving the players fair hole locations," he said. "We are using a Stimpmeter to review the speeds on these greens several times a day."

Speeds are running between 13.5 and 14.5 on the Stimpmeter  - very fast considering the tilt and undulations.

"We also used a digital level in our review of the hole locations," Hyler said. "We are reviewing the slopes, the grade of the slopes all around the holes and then the run-offs.

"We are approaching these greens this week very carefully...to make sure that we don't get over the edge."