Luanda in Angola is the most expensive city in the world for expatriate professional migrants to live. As opposed to Hong Kong, everything in Luanda is expensive as almost all international standard goods and services are imported. Despite the lower oil price, the slow-down in oil related projects, and dramatic reduction in revenue to Angola in 2016, prices in Luanda remain extremely high.

Hong Kong is the second most expensive city due to the very high cost of housing and healthcare, as well as the strong Hong Kong dollar which is fixed against the US Dollar. An interesting observation is the fact that if 4 of the 13 baskets are excluded from the cost of living index calculation (namely Housing, Education, Medical and Transport) then Hong Kong drops out of the top 10 most expensive cities in the world. This illustrates that not everything in Hong Kong is expensive. It is therefore very important it is to ensure that the correct baskets are included in an expat cost of living index.
https://www.xpatulator.com/cost-of-living-article/International-City-Cost-of-Living-for-Expatriate-Professional-Migrants_716.cfm