Our Lord showed Saint Gertrude the Great that the following prayer would release a vast number of souls from purgatory each time it is said.

Eternal Father, I offer Thee the most Precious Blood of Thy Divine Son, Jesus, in union with the Masses said throughout the world today, for all the Holy Souls in purgatory.  Amen

Approval of His Eminence the Cardinal Patriarch of Lisbon, April 2, 1936.

(This prayer was extended to include living sinners by adding...For sinners everywhere, for sinners in the universal church, those in my own home and within my family.  Amen.)