Germany's Lanxess sold 50 percent of its synthetic-rubber business, the world's largest, to Saudi Aramco, partnering with the leading oil firm to gain better access to petrochemical raw materials.

The deal values the joint venture that the two companies will set up in the Netherlands at 2.75 billion euros ($3.1 billion) and operational control will be assumed by Lanxess, the German group said in a statement.

State oil company Saudi Aramco, which has been branching out into more advanced chemicals, will buy the stake for around 1.2 billion euros in cash.

Lanxess Chief Executive Matthias Zachert said teaming up with a supplier of petrochemicals used in synthetic rubber meant following the example of its main rivals and this would cut exposure to swings in that market.

Lanxess was the last among the world's 10 largest rubber groups that had no affiliation with either a supplier of petrochemical raw materials or with a tyre group, Zachert told journalists on a call.

"But we're drawing level with phenomenal firepower. The number one in rubber is merging with the number one in energy."

Its competitors in synthetic rubber include Exxon Mobil, which is working with Sabic, Eni's chemicals arm Versalis and Michelin collaborating with Indonesian petrochemical company Chandra Asri.

Sources have told Reuters that Lanxess also held talks with European petrochemicals group Ineos, Russia's NKNK and Sibur.

The search for a strategic partner for the German group's synthetic rubber business, the world's largest with about 3 billion euros in sales, began more than a year ago as the company sought to combat oversupply in the industry.

Lanxess shares extended gains on the news and were up 3.1 percent at 1245 GMT as market participants applauded the price.

Analyst Markus Mayer at Baader Bank said Lanxess stood to fetch about 10 percent more than what the business was worth based on his sum-of-the-parts analysis.

The 2.75 billion euro valuation, which includes debt, amounts to 7.3 times estimated 2015 earnings before interest, taxes, depreciation and amortization (EBITDA), Mayer added.