Brunei is one of the wealthiest countries in the world. It is typical of small rich countries such as Monaco, Qatar, Lichtenstein, Singapore, Luxembourg and Switzerland; each of which has a special market position and cultural history.
Over 70% of Brunei wealth is linked to oil and petroleum industries.
Only about 1% of the population is engaged in agriculture.
There are also massive services, financial and corporate sectors involving global companies and foreign governments.
The GDP [nominal] per head of population exceeds US$54,000 and this is bigger than the USA figure. In other words, the average person in Brunei is richer than an American. This places Brunei at 11th position in the world. [USA is at 14th position.]
Also, there is an excellent provision for free schools, dental and health care, elderly and disabled support, cheap transport and subsidized food. All this is based on the taxation income of the Sultan's government, which is used for the people of the country.
Taxes account for 40% of GDP, almost all from corporations and foreign investors.
Government expenditure accounts for about one-fifth of all consumption.
The cost of living [prices] is about 68% of the USA figure; whereas the typical household expenditure is higher.
In Australia, the GDP per head is about US$42,000; almost 20% lower than Brunei.
This places Australia at position 18th in the world.
Government expenditure accounts for about one-seventh of all consumption.
Taxes account for 32% of GDP; about half from individuals and households.
The cost of living [prices] is higher at about 112% of the USA figure; whereas the typical household expenditure is much lower.
Overall, the standard of living in Brunei is much higher than in Australia, for the typical household.
And higher than most other places in the world.
BUT you haven't asked about the quality of life; the freedoms, openness, religious tolerance, social mobility, aristocratic dominance and so on. They all make a difference but you didn't ask in this question.