Shoulder problems have limited the big right-hander to 22 Major League starts over the past three seasons, but he says those issues are behind him now and he threw well at the end of last season in Triple-A ball and again in the Dominican Winter League.
McCarthy, 27, agreed to a $1 million deal that includes further incentives if he stays healthy and performs well.
"Everything right now is 100 percent," McCarthy said as he prepared to fly home to Dallas after meeting with A's officials. "No issues have come back up. I just revamped my whole shoulder program and Texas took care of me as well as they could.
"Toward the end of last year I never felt any problems again and that carried over to the Dominican. Right now I'm as positive as I can be."
The 6-foot-7 McCarthy said he's never had surgery on his shoulder, but has been bothered by micro stress fractures in the back of his shoulder blade. He said now that doctors know what they're dealing with, he's going with a new routine and hoping the issue is in the past.
He has a 20-24 record and 4.56 ERA over five seasons with the White Sox and Rangers and was 7-4 with a 4.62 ERA in 17 starts for Texas in '09 before the problem flared up again. He was 4-2 with a 3.36 ERA in 11 appearances for Triple-A Oklahoma City in the Texas Rangers organization last year.
If healthy, he could provide further depth to an Oakland pitching staff that posted the lowest ERA in the American League last year. McCarthy made four starts in the Dominican Winter League and was 2-0 with a 1.96 ERA.
"This is a good setup," he said of the A's. "Over the last few years I've had a chance to see them up close in the AL West and I know how much young talent and cool young clubhouse they've got.
"I hope to just fit in that rotation. Watching [Brett] Anderson and [Trevor] Cahill and [Dallas] Braden and Gio [Gonzalez] the last few years, those are guys with great stuff and composure. My job is to fit in wherever they need me. I'd definitely love and prefer starting and hopefully I can get that fifth spot and hold the line there."
McCarthy was originally selected by the White Sox in the 17th round of the '02 Draft and spent two years in the Major Leagues with Chicago before being traded to the Rangers in '06.
This was his first shot at free agency and he said the experience was interesting.
"A lot of teams checked in and everybody was doing research on the medical issue," he said. "I got some good offers, but Oakland was the best fit. It had everything we needed. It's a great pitcher's ballpark and they showed a good commitment to me. Plus I'm a huge soccer fan and their front office is obsessed with soccer, so that was good to go with it."
Now the key will be kicking his own injury history and proving he's able to be a consistent starter in the Major Leagues once again.
Based on his recent run, the big man feels he's ready. He closed out his season strong at Oklahoma City and carried that over with Toros del Este in the Dominican Winter League.
"That was a good test," he said. "Everything felt good that last month [in Triple-A]. I was throwing 100 pitches a start and bouncing back five days later. That's why I was excited to get back to the Dominican and keep that going.
"And once I got there, no problems. That was a cool experience and just kind of boosted my confidence, knowing we're on the right page and everything feels good."