The score was tied at 3-3 heading into the final period, when the Oilers poured it on to win for the third time in four outings. Chicago has lost four in a row.
Gagner scored on a slap shot 1:54 into the third to give the Oilers a 4-3 lead and Cam Barker tallied for Edmonton 1:49 later. After Dave Bolland brought Chicago back within one, Gagner produced his third and fourth goals of the game to give him nine for the season.
Devan Dubnyk gave up four goals on 47 shots, but still picked up the victory.
It was the second time this season Edmonton had produced an offensive outburst against Chicago. The Oilers defeated the Blackhawks 9-2 Nov. 19.