KASSEL, Germany (Reuters) - BASF oil and gas subsidiary Wintershall on Wednesday said it expects a significant rise in sales and earnings before special items in 2018 after increasing both measures steeply last year thanks to higher gas prices.

Chief Executive Mario Mehren at a press conference in Kassel said that production would rise again in 2018 in the company's key areas Norway, Argentina and Russia, driving growth after stagnant output volumes last year.

"The decisive factors will be positive price effects as well as higher production from newly started fields especially in Norway," he said.

Oil prices last year increased 23 percent to $54 per barrel on average for North Sea grade Brent. Wintershall's planning is based on an average $65 (46.86 pounds) this year and an exchange rate of $1.2 per euro.

It also sees gas prices remaining at the current levels in north-western Europe in 2018 after spot gas at European trading hubs rose 24 percent last year.

Wintershall's parent BASF had reported results on Feb. 27, with Wintershall accounting for 9.5 percent of the group's adjusted EBIT and 5 percent of sales.

A planned merger with Russian-owned German peer DEA will likely close by the end of third quarter 2018.

(Reporting by Vera Eckert, editing by Ludwig Burger)

Stocks treated in this article : BASF, Gazprom PAO