Blót
It is attested in primary sources that sacrifices were made to Odin during blóts. Adam of Bremen relates that every ninth year, people assembled from all over Sweden to sacrifice at the Temple at Uppsala. Male slaves and males of each species were sacrificed and hung from the branches of the trees.
As the Swedes had the right not only to elect their king but also to depose him, the sagas relate that both King Domalde and King Olof Trätälja were sacrificed to Odin after years of famine. It has been argued that the killing of a combatant in battle was to give a sacrificial offering to Odin. The fickleness of Odin in war was well documented; in Lokasenna, Loki taunts Odin for his inconsistency.
Sometimes sacrifices were made to Odin to bring about changes in circumstance. A notable example is the sacrifice of King Víkar that is detailed in Gautrek's Saga and in Saxo Grammaticus' account of the same event. Sailors in a fleet being blown off course drew lots to sacrifice to Odin that he might abate the winds. The king himself drew the lot and was hanged.
Sacrifices were probably also made to Odin at the beginning of summer (mid April, actually—summer being reckoned essentially the same as did the Celt, at Beltene, Calan Mai, which is Mayday—hence as summer's "herald"), since Ynglinga saga states one of the great festivals of the calendar is at sumri, þat var sigrblót "in summer, for victory;" Odin is consistently referred to throughout the Norse mythos as the bringer of victory. The Ynglinga saga also details the sacrifices made by the Swedish king Aun, to whom it was revealed that he would lengthen his life by sacrificing one of his sons every ten years; nine of his ten sons died this way. When he was about to sacrifice his last son Egil, the Swedes stopped him.
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