the bar "The Oasis" in Concordia, Kansas was mentioned in a song that was released on which date ? 
Jim Garver:  Garver is credited with naming the bar "The Oasis" (after a closed establishment in his hometown of Concordia, Kansas) in the song "Friends in Low Places" made famous by Garth Brooks. Friends in Low Places:  It was released on August 6, 1990 as the lead single from his album "No Fences".
August 6, 1990