Hi Guys:
"Mercy, Mercy, Mercy" is a song (now considered a Jazz Standard) written by Jazz pianist, Joe Zawinul in 1966 for the great alto saxophonist, Julian Edwin "Cannonball" Adderley for his album, "Mercy, Mercy, Mercy! Live at 'The Club'". The song is the title track of the album and became a surprise hit. "Mercy, Mercy, Mercy" went to #2 on the Soul chart and #11 on the Billboard Hot 100 chart.
Check out Joe Zawinal and his band: 
For The Musicians:
The first part of the theme is played two times and is completely made of notes from the major pentatonic scale of the first degree. The tune is in the key of B-flat major and has a 20-bar structure with four distinct sections. The chord progression is mainly made of dominant-seventh chords on the first, fourth and fifth degrees,giving the song a bluesy feeling; although it does not follow a typical blues progression. In particular, the subdominant (IV) chord in the beginning section emphasizes the bluesy feeling. In the second section, the tonic chord alternates with a second-inversion subdominant chord.
So, here is my interpretation of the tune. Hope you enjoy...
Griff