Australian health insurer Medibank made its stock market debut after raising A$5.679bn (£3.1bn; $4.9bn) in Asia’s biggest public offering in two years.
Tuesday’s listing on the Australian Securities Exchange was the biggest of a state-owned asset in 18 years.
Shares first traded at a premium of A$2.22, compared to A$2.15 that institutional investors had paid and A$2 that retail investors paid.
The move was part of the government’s plan to sell A$130bn in assets.
Traders had said shares would sell 13% higher than the price that 440,000 retail investors, who own 60% of the firm, paid to subscribe to the listing.
Medibank’s shares are appealing for investors keen to gain exposure to Australia’s booming health industry, which benefits from generous state subsidies and is boosted by a wealthy ageing population.
The debut was the largest share offer of a state firm since the government sold Telstra in 1997.
The country’s largest private health insurer was set up in 1975 by Australia’s Health Insurance Commission, now known as Medicare Australia.
Analysis: Phil Mercer, BBC Sydney Correspondent
It’s Australia’s most anticipated share offer of the year.
Small investors are expected to be among the winners when Medibank, the country’s largest private health insurer, floats on Tuesday.
A legion of bargain hunters has snapped up stock for A$2, a slight discount to the A$2.15 offered to institutional buyers.
Experts predict that shares will soar when trading begins at midday Sydney time (0100 GMT), and there is an expectation their value will climb to A$2.50 by the end of the year.
Another big winner is Australia’s federal government. The privatisation of such a valuable and well-known asset has raised A$5.67 billion.
The Belgian-born Finance Minister Mathias Cormann says the cash will be ploughed into infrastructure and would generate a wealth of jobs.
Medibank was set up in the mid-1970s to compete in Australia’s private insurance market.
It has been a lucrative enterprise, although net profits slipped from A$232.7m in 2012/13 to A$130.8m in the year to June.