I was looking at the stock time series of ExxonMobil (traded as XOM) on Yahoo Finance and I noticed that it starts from 1962, while the IPO was in 1978 and the fusion of Exxon and Mobil took place in 1998. How can a company be listed before birth? And if it were possible, what would be the price before the fusion (or before the the IPO)?
Exxon came public as an IPO in 1978. It has traded before, during and since. While it may be called a merger, Exxon swallowed Mobil as an acquisition, with Mobil shareholders receiving some multiple of Exxon shares for every share of Mobil held.
There was no exchange traded price before the IPO because it wasn't a publicly traded company until the IPO.
Formally, Mobil was bought by Exxon. Mobil's shareholders received 1.32 Exxon's share for each Mobil's share. As a result, the former Mobil's shareholders receives about 30% in the merged company while the stake of former Exxon's shareholders was about 70%.
Assuming the shares that Mobil shareholders received were newly issued, this means that one post-merger ExxonMobil share can be considered to be equal to .7 Exxon pre-merger shares plus .227 Mobil pre-merger shares. That is, if before the merger, you had 700 Exxon shares and 227 Mobil shares, your Mobil shares would turn into 300 ExxonMobil shares, giving you 1000 total ExxonMobil shares. Thus, the ExxonMobil equivalent of pre-merger shares can be calculated by taking .7*(Exxon share price)+.227*(Mobil share price).