6:40pm: The signing is official, the team has announced. Forward Ryan Reid has been waived to clear a roster spot for Fisher.
4:13pm: Derek Fisher and the Thunder have agreed to terms on a contract that will bring the point guard to Oklahoma City for the rest of the season, reports ESPN.com's Marc Stein. Fisher is due to clear waivers within an hour, at which point the two sides are expected to finalize the deal.
According to Stein, Oklahoma City's financial flexibility was a factor in giving them the edge over the Heat for Fisher's services. The Thunder still have a good portion of their mid-level exception remaining, and can offer Fisher part of that amount. The Heat could only have offered the 37-year-old a pro-rated portion of the veteran's minimum.
Fisher joins the Thunder after having been traded by the Lakers and then bought out by the Rockets. In 43 games for the Lakers this season, he averaged 5.9 PPG and 3.3 APG in 25.6 MPG, but became expendable when Los Angeles acquired Ramon Sessions.
The Thunder are scheduled to travel to the Staples Center to face the Lakers on March 29th and April 22nd, so Fisher will get multiple opportunities to face his former team, even if the two clubs don't meet in the postseason.