MOSCOW, July 18 (Reuters) - The Russian rouble strengthened against the dollar on Thursday, helped by rising oil prices and a weakening dollar.

Sanctions on Moscow Exchange and its clearing agent, the National Clearing Centre, led to varying prices and spreads as trading shifted to the over-the-counter (OTC) market on June 14, obscuring access to reliable pricing for the Russian currency.

Against the yuan, which had already become the most-traded foreign currency in Moscow before the latest sanctions were imposed, the rouble was down 0.1% at 12.01, according to an analysis of the OTC market.

It was up 0.3% at 96.50 against the euro.

Brent crude oil, a global benchmark for Russia's main export, was up 0.7% at $85.75 a barrel, buoyed by a bigger-than-expected decline last week in crude stocks in the United States, the world's largest oil consumer.

The market is also expecting major Russian exporting companies to start converting their foreign currency earnings into roubles ahead of the monthly corporate tax payments on July 29. This conversion should provide further support for the rouble. (Reporting by Gleb Bryanski; Editing by Arun Koyyur)