It is a Vedic sacrificial rite. Though considered as an independent rite, it is actually incorporated in the Somayāgas like the Agniṣṭoma. It is generally performed twice a day for three days.
An important item of this sacrifice is the preparation of gharma (hot milk mixed with boiling ghee) out of the milk of a cow and a she-goat, along with ghee.
The offerings of gharma are made through fire to the deities Aśvins, Vāyu, Indra, Savitṛ, Bṛhaspati and Yama.
The sacrificer drinks the remainder from the upayamanī (the supporting ladle used in the oblations).
During the performance of the Pravargya rite, the doors of the prācīna-vaṁśa or the sacrificial shed are kept closed.