The European Union was preparing a ban on Russian oil, with possible exemptions for wary countries, as EU energy ministers on Monday held crisis talks on Moscow’s demand that foreign buyers pay for gas in rubles or lose their supply. The European Commission is expected to propose a sixth package of EU sanctions this week against Russia over its invasion of Ukraine, including an embargo on buying Russian oil – a measure that would deprive Moscow of a large revenue stream, but that has so far divided EU countries. Russia supplies 40 percent of EU gas and 26 percent of its oil imports. To keep th…