In 995, rumours began to surface in Norway about a king in Ireland of Norwegian blood. This caught the ear of Jarl Haakon, who sent Thorer Klakka to Ireland, posing as a merchant, to see if he was the son of Tryggve Olafson. Haakon told Thorer that if it were him, to lure him to Norway, so Haakon could have him under his power. Thorer befriended Olaf and told him of the situation in Norway, that Jarl Haakon had become unpopular with the populace, because he often took daughters of the elite as concubines, which was his right as ruler. He quickly grew tired of them and sent them home after a week or two. He had also been weakened by his fighting with the Danish king, due to his rejection of the Christian faith.
Olaf seized this opportunity, and set sail for Norway. When he arrived many men had already started a revolt against Haakon, who was forced to hide in a hole dug in a pigsty, together with one of his slaves Kark. When Olaf met the rebels they accepted him as their king, and together they started to search for Haakon. They eventually came to the farm where Haakon and Kark were hiding, but could not find them. Olaf held a meeting just outside the swine-sty and promised a great reward for the man who killed the Jarl. The two men in the hole heard this speech, and Haakon became distrustful of Kark, fearing he would kill him to claim the price. He could not leave the sty, nor could he keep awake forever, and when he fell asleep Kark took out a knife and cut Haakon's head off. The next day the slave went to meet Olaf and presented with the head of Haakon. The king did not reward him, and instead beheaded the slave.
After his confirmation as King of Norway, Olaf traveled to the parts of Norway that had not been under the rule of Haakon, but that of the King of Denmark; they too swore allegiance to him. He then demanded that they all be baptised, and most reluctantly they agreed.
In 2009, the worldwide capacity for producing formic acid was 720,000 tonnes/annum, roughly equally divided between Europe (350,000, mainly in Germany) and Asia (370,000, mainly in China) while production was below 1000 tonnes/annum in all other continents. It is commercially available in solutions of various concentrations between 85 and 99 w/w %. As of 2009, the largest producers are BASF, Eastman Chemical Company, LC Industrial, and Feicheng Acid Chemicals, with the largest production facilities in Ludwigshafen (200,000 tonnes/annum, BASF, Germany), Oulu (105,000, Eastman, Finland), Nakhon Pathom (n/a, LC Industrial) and Feicheng (100,000, Feicheng, China). 2010 prices ranged from around 650/tonne (equivalent to around $800/tonne) in Western Europe to $1250/tonne in the United States.