The Phillies released Willis last week after he allowed five runs and five hits, and walked four batters, in 2 2/3 innings.
Executive vice president Dan Duquette confirmed that the Orioles are working on a minor league deal, but he didn't offer any specifics.
Asked if the deal would include a late spring training invite, Duquette replied, "We're working on that part."
ESPN's Jerry Crasnick first reported that the Orioles would sign Willis, 30, who went 1-6 with a 5.00 ERA in 13 starts with the Reds last year.
Willis is 72-69 with a 4.17 ERA in nine major league seasons. His best year by far was 2005, when he went 22-10 with a 2.63 ERA in 34 starts with the Marlins and finished second in the National League's Cy Young voting. He's won only four games since 2008 and continues to have control issues.
Left-handers batted .127 against him last season. Maybe he's viewed as a lefty specialist. Or a reclamation project.
Update: According to The Sun, it's a split contract worth $700,000 if he reaches the majors. We should see him in Sarasota tomorrow.
Willis' agency, Sosnick Cobbe Sports, tweeted confirmation that he signed a minor league deal.
Update II: It appears that the Orioles view Willis as a reliever at this point.