Germany's Wintershall has made what could be a major oil discovery in the Dutch North Sea, pending appraisal drilling in 2013, the company said on Tuesday.

Wintershall, the exploration arm of chemicals group BASF, said it had found at least an estimated 30 million barrels of recoverable oil in September in the exploration licence F17a.

This lies about 120 kilometres north of the port of Den Helder.

Wintershall is already one of the largest gas producers in the southern part of the North Sea and had not been targeting oil for a while, said Gilbert van den Brink, managing director of Wintershall Noordzee, the operator of the licence.

"This discovery gives us the opportunity to grow our business in the Netherlands and provide a more balanced portfolio in term of oil and gas," he said.

Other partners in the licence are Dutch state-owned EBN, GDF Suez E&P Nederland, Rosewood Exploration and TAQA Offshore.

Early in 2012, Wintershall launched tight gas production from the K18-Golf field in the Dutch North Sea. It is also exploring in the British, German and Danish North Sea.