President John Atta-Mills opened the valves in a ceremony on a floating platform 60 kilometres off Ghana's coast.
"This should be a blessing and not an oil curse," he said later.
The fields were discovered almost four years ago and are estimated to contain more than a billion barrels of oil.
It is thought the oil will bring in more than $400 million of revenue during the first year.
Ghana Becomes an Oil Nation
But some analysts are concerned about Ghana's ability to manage its new industry.
Commercial production comes while proposed laws to regulate the industry still under debate in parliament.
Critics also argue that Ghana does not yet have the infrastructure to tap the gas that comes with crude production.
Ghana Becomes an Oil Nation
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