Global stock markets were heading for their best week of the year on Friday following reassuring company results, encouraging data from the world's biggest economies and signs the ECB is upping its efforts to lift Europe.

European bank stress-test results due at the weekend and confirmation of New York City and Mali's first cases of Ebola saw a touch of caution return, though markets were just happy to have broken out of a steep month-long selloff.

Wall Street's S&P 500 .SPX was set to open around 0.25 percent lower partly on the Ebola jitters and partly on profit taking. It was still heading for a weekly gain of over 3 percent, it's biggest since December last year.

The MSCI 45-country world index .MIWD00000PUS was set for its strongest run since last July and oil was on track for its first rise in five weeks, having been battered recently by a combination of global growth and oversupply worries.

"This week has been pretty crazy," said Kully Samra a managing director at U.S. trading firm Charles Schwab in London.

"It's has been the strongest week of the year for stocks, we have seen triple digit moves (in points) on the Dow and the volumes have been very, very strong, well above a billion."

Before U.S. trading, European shares were paring their early losses as investors took a more relaxed view of the Ebola cases and bet Sunday's bank stress-test results would not expose any horror stories but would be credible enough to ensure repairs in the sector continued.

Banking stocks were the day's outperformers, rising 0.3 percent compared with falls of 0.3-0.6 percent on the main bourses in London .FTSE, Frankfurt .GDAXI and Paris .FCHI.

It has been an intense, year-long process for the ECB, and leaks have begun to filter out. Spanish news agency Efe reported that at least 11 banks from six European countries were set to fail the review.

The euro EUR= was hovering flat at $1.2638, while southern euro zone bonds for the most part enjoyed a dip in yields. Both had fallen for much of the week after European Central Bank insiders told Reuters the bank was drawing up plans for a corporate bond purchase program.

BEST WEEK OF YEAR

The Ebola fears saw S&P 500 mini futures ESc1 dip 0.25 percent, but U.S. markets are at two-week highs on budding optimism from corporate earnings and the global economy.

So far, 177 of the S&P 500 companies have posted third-quarter results and 69.5 percent have beaten expectations. That was better than the 67 percent rate over the past four quarters and higher than the 20-year average of 63 percent, Thomson Reuters data showed.

There was also focus on Russia and Ukraine, with Russia facing a rating review from Standard & Poor's after markets close and elections taking place in Ukraine on Sunday.

The rouble was at a record low and stocks were in the red before the S&P review, which could cut Russia's credit rating cut to 'junk'. Moscow, however, hopes its solid finances will avoid a downgrade, which would be the second downgrade from a major rating agency in as many weeks.

"I would assume that it is too early to revisit the ratings. But this is my personal opinion. The rating agencies work according to their methodologies," a former Russian finance minister and outspoken policy critic, Alexei Kudrin, told Reuters at an event in London this week.

ELECTION FEVER

Greater political stability in Ukraine could aid the broader European economy, which has suffered from the drop in trade with Russia on tit-for-tat sanctions between the West and Moscow.

"I suspect one often overlooked reason for the market's rebound since the middle of this week was signs of easing tensions between Russia and Ukraine," said Soichiro Monji, chief strategist at Daiwa SB Investments.

President Petro Poroshenko's bloc holds a big lead ahead of Sunday's poll in Ukraine, but populist Oleh Lyashko's Radical party could also make a strong showing.

If so, it would put Poroshenko in the awkward position of seeking support from a politician who has been sharply critical of his peace plan and contacts with Russian President Vladimir Putin.

Brazil also holds the second round of its elections. The Bovespa stock index .BVSP hit a six-month low while the Brazilian real slumped to a 9-1/2-year low on Thursday as markets wagered current President Dilma Rousseff is likely to beat rival Aecio Neves, who is seen as more market-friendly.