President Recep Tayyip Erdogan told reporters that the drilling ship Fatih, which has been operating in the area since July, had found 320bn cu m (11.3 tr cu ft) of gas.
He said it was Turkey's biggest natural gas find to date.
If Turkey can extract the gas commercially, it will be able to reduce its reliance on imported energy.
President Erdogan said all tests and engineering work had been completed.
He added: "This reserve is actually part of a much bigger source. God willing, much more will come.
"There will be no stopping until we become a net exporter in energy."
President Erdogan said he hoped to start extracting the gas by 2023.
But energy experts say it could take up to a decade and billions of dollars of investment to get the gas into commercial use.
source : https://www.bbc.co.uk/news/business-53866217