The Holy Souls in purgatory are incapable of helping themselves.  They depend on the works of mercy by the living and the mercy of Jesus and Mary to shorten their time in purgatory.  Their souls are very dear to God's Heart.  He is most generous to those who offer every good act, suffering, prayer or Holy Mass for these souls.  In gratitude they intercede for us.

(Saint John Vianney once said, "The good God will render us back the good we do for them (poor souls) a hundred fold.")

On August 16, 1969, in San Damiano, Italy, Our Lady asked that we pray very much for the poor souls and that if we pray these prayers, we'll "deliver so many souls, so many souls!"

Pray 

Five Apostles' Creed  

I believe in God the Father Almighty, Creator of Heaven and Earth, and in Jesus Christ, His only Son, our Lord, who was conceived by the Holy Spirit, born of the Virgin Mary, suffered under Pontius Pilate, was crucified, died and was buried.  He descended into hell.  The third day He rose again from the dead.  He ascended into Heaven and sits at the right hand of God the Father Almighty.  From there He shall come to judge the living and the dead. 

I believe in the Holy Spirit, the Holy Catholic Church, the communion of Saints, the forgiveness of sins, the resurrection of the body and life everlasting.  Amen.

One Salve Regina (Hail, Holy Queen)

Hail, Holy Queen, Mother of mercy; hail, our life, our sweetness and our hope.  To thee do we cry, poor banished children of Eve.  To thee do we send up our sighs, mourning and weeping in this vale of tears.  Turn then, most gracious advocate, thine eyes of mercy towards us and after this our exile show unto us the blessed fruit of thy womb, Jesus.  O clement, O loving, O sweet Virgin Mary.

Pray for us O Holy Mother of God, that we may be made worthy of the promises of Christ.

One Our Father

Our Father, Who art in Heaven, Hallowed be Thy name.  Thy Kingdom come, Thy will be done on Earth as it is in Heaven.  Give us this day our daily bread, and forgive us our trespasses, as we forgive those who trespass against us, and lead us not into temptation, but deliver us from evil.   Amen.

One Hail Mary

Hail Mary, full of grace, the Lord is with Thee.  Blessed art Thou among women and blessed is the fruit of Thy womb, Jesus.  Holy Mary, Mother of God, pray for us sinners now and at the hour of our death.  Amen.

One Glory Be

Glory Be to the Father, and to the Son, and to the Holy Spirit.  As it was in the beginning, is now and ever shall be; World without end.  Amen.

One Requiem

Eternal rest grant unto them O Lord and let perpetual light shine upon them and may they rest in peace.  Amen!

Requiem Indulgenced by Pope Leo XIII, March 22, 1902