Details are being finalized, though the teams have agreed to terms, a baseball source told Olney. The Associated Press, citing two people with knowledge of the talks, reported on Tuesday that the teams were reviewing the physicals of the players involved and an announcement was anticipated early Wednesday.
The deal is also pending completion of physical exams.
"Talks are continuing. They're very fluid and at this point, everything's speculation," Rockies spokesman Jay Alves said, speaking on behalf of general manager Dan O'Dowd.
Oakland owner Lew Wolff, attending a regional luncheon of Associated Press sports editors, wouldn't confirm or deny a trade but said he had already spoken with general manager Billy Beane three times on Monday.
"Billy's doing different things right now," Wolff said.
Pitcher Greg Smith, who was 7-16 with a 4.16 ERA last season for the A's, is one of the players in the deal, a source confirmed to Crasnick.
"I don't know how official everything is," Smith said, according to the San Francisco Chronicle. "All I know is I've been called, and I'm flying to Denver probably tomorrow."
The Rockies have a need for late-inning relief with Brian Fuentes about to leave through free agency.
"They just called me a little while ago and told me the deal's in place," Gonzalez said, according to USA Today. "It surprised me, but that's how baseball works. You're always subject to be traded."
Gonzalez, 23, saw his first big league action last season and hit .242 with four home runs and 26 RBIs in 302 at-bats.
David Forst, Oakland's assistant general manager, declined to comment on the trade.
"It's still an ongoing discussion,'' he said.
The news comes a day after reported trade talks between the Colorado Rockies and St. Louis Cardinals broke down. The Cardinals had reportedly offered the Rockies a package for Holliday that was centered around outfielder Ryan Ludwick, who hit 37 home runs last season.
Holliday, 28, finished second to Philadelphia's Jimmy Rollins in the 2007 National League MVP balloting. He hit .321 with 25 homers and 88 RBIs last season and will be eligible for free agency next winter. Holliday is represented by Scott Boras, so the Rockies held out little hope to sign him to a long-term deal.
Holliday, playing half his games at Coors Field, has 128 homers and 483 RBIs in five big league seasons. His best year was 2007, when he won the NL batting title with a .340 average and had 36 homers and a league-best 137 RBIs in helping the Rockies reach the World Series.
Oakland was last in the major leagues with a .242 batting average this season and last in the AL with 646 runs.
"If we can bring a little bit of hitting talent to our current team I think the pitchers won't get as frustrated as they were late in the season," Wolff told the gathering of sports editors. "You're always rebuilding and regenerating. It's fun. We want to win. I want to win. We're going to try to be there again if we can."
The A's used eight starters in left field and finished 75-86, their worst record since 1998. Oakland advanced to the AL Championship Series in 2006 before being swept by the Detroit Tigers.
Information from ESPN.com baseball writer Jerry Crasnick, ESPN The Magazine's Buster Olney and The Associated Press is included in this report.