The team announced the news on their Twitter account Thursday, with Oswalt expected to report to extended spring training.
The 35-year-old Oswalt has a career record of 163-96. He's also 4-0 with a 2.25 ERA at Coors Field.
On his Twitter account, Oswalt tweeted: "Always loved the mountains, im back!"
Oswalt hasn't pitched in the majors since Oct. 2, when he was with the Texas Rangers. He's also played for Houston and Philadelphia.
The first-place Rockies certainly could use a boost on the mound with righty Jhoulys Chacin on the 15-day disabled list due to a strained lower back.
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