There is big and there is humungous. On Friday, the world’s biggest company by market capitalisation was worth just below $500bn. By Monday, the new holder of the crown boasted a market capitalisation of more than twice that. Benchmarked against almost anything, PetroChina’s value is huge. It is worth more than Exxon Mobil and General Electric combined, roughly equivalent to the entire Brazilian economy, and worth substantially more than the combined economic output of the five founding members of the Organisation of the Petroleum Exporting Countries.

The reality is less eye-popping. PetroChina, one of China’s three oil and gas majors, acquired its $1,000bn-plus market capitalisation on the back of a listing on China’s domestic “A” share market, which routinely attributes sky-high valuations to issuers. No wonder: issuers are parsimonious with stock – PetroChina’s mainland free float is a minuscule 2 per cent – and mainland Chinese investors are essentially restricted to buying shares at home. Such favourable supply and demand dynamics explain why the Shanghai market is trading at around 50 times earnings. Pricing the roughly 86 per cent of shares that are held by the state at the slightly saner Hong Kong price gives PetroChina a market cap of $420bn, behind Exxon Mobil.