"We're looking at an amount in the hundreds of millions for the exploration phase," Gernot Kalkoffen, the board chairman of Exxon Mobil Central Europe told business daily Handelsblatt.
Previously, nine companies had announced plans to drill in the region, once the heartland of Germany's coal industry.
In November, the WAZ media group reported that US oil company Exxon Mobil, along with energy firms from Australia, Canada and Germany, had been granted permission by the state to conduct test drilling that would cost millions.
But how high that sum might be depends on the concentration of natural gas reserves in the state and whether mining them proves profitable.
Kalkhoffen said a successful venture could result in more than €1 billion in investment.
The nine companies looking to drill in North Rhine-Westphalia have secured options for different areas of the state. With gas deposits in rock strata estimated at 2,100 billion cubic metres, the site could prove to be Europe's second largest store of natural gas.
Handelsblatt said drilling in NRW would bring in profits and create new jobs. In Lower Saxony, where natural gas has been mined for years, about 7,000 jobs were created as a direct result of the industry, as well as some 20,000 secondary positions.
"In Lower Saxony, up to a €1 billion in royalties have been paid in previous years," Exxon Mobil's boss in Europe said.