The sides have an agreement in principle, according to the report on a five-year deal worth a maximum $60 million. Agents were permitted to talk to teams about their clients Monday at noon ET, although no contract can be signed until after the league year begins.
The Raiders are among the teams with the most money under the salary cap, and as of Tuesday they were more than $60 million under the league's spending limit.
Osemele, 26, is considered one of the most physical and versatile offensive linemen in free agency. He boosted his value last season when he switched from left guard to left tackle for the last four games. Osemele was also the Ravens' starting right tackle in the Super Bowl in 2012.
A second-round pick in 2012, Osemele built a reputation as a mauling run-blocker and sound pass-protector. He gave up one sack and 10 quarterback hurries last season, but his play often got overshadowed by guard Marshal Yanda, a five-time Pro Bowl lineman.
Ravens officials said they made an "aggressive" offer to Osemele at the NFL scouting combine, but Baltimore was unable to keep him out of free agency. Osemele was one of two Ravens starters who were unrestricted free agents; linebacker Courtney Upshaw was the other.
ESPN Ravens reporter Jamison Hensley contributed to this report.