KIEV, Sept. 16 - French natural gas company Gaz de France (GDF) may start storing undisclosed amount of gas in Ukrainian underground gas tanks, according to a preliminary agreement reached earlier this week, a Naftogaz Ukrayiny official said.

Naftogaz, which has some of the biggest underground gas tanks in Europe, has been so far rendering storage services to Russian gas giant Gazprom, but started to look for new customers after Gazprom had indicated it may reduce the practice.