One of the most popular prayers for the Holy Souls in Purgatory is traditionally attributed to St. Gertrude the Great:  "Eternal Father, I offer You the Most Precious Blood of Your Divine Son, Jesus, in union with the Masses said throughout the world today, for all the Holy Souls in Purgatory, for sinners everywhere, for sinners in the Universal Church, those in my own home, and within my family. Amen." (Marian Press: #EOGPF)