The Diocesan Chrism Mass, or Mass of the Oils, takes place on the Tuesday of Holy Week in St John's Cathedral, Portsmouth, normally at 11.00am. It is the most important diocesan celebration of the year. The Bishop is surrounded by his priests, deacons and people from all over the diocese. The singing of the congregation is supported by a large Diocesan Choir.

The Cathedral is always packed, more and more people coming each year because they know what a marvellous celebration it is.

Before Vatican II, the Chrism Mass used to take place on Maundy Thursday morning. These days it is held at a time which enables clergy and people from across the diocese, including the Channel Islands, to be there and to return home without disrupting other Holy Week services. Before Vatican II, the Chrism Mass was the occasion when the oils were solemnly blessed: the Oil of the Sick, the Oil of Catechumens and the Oil of Chrism from which the Mass takes its name. As its name suggests, the Oil of the Sick is used to anoint the sick. The Oil of Catechumens is used in the rites of initiation, including infant baptism. Chrism is also used at baptisms, confirmations, ordinations, and in the rite of dedication of a church or altar.

In 2011 the Chrism Mass will take place on Tuesday 19 April.