(Adds U.S. market open, byline, dateline; previous LONDON)

* Wall St. gains on dovish Yellen remarks

* Dollar slides after Yellen makes no monetary policyremarks

* Oil gains as U.S. Gulf

By Herbert Lash

NEW YORK, Aug 25 (Reuters) - World stock markets advancedwhile the U.S. dollar weakened on Friday after Federal ReserveChair Janet Yellen omitted monetary policy in a much-anticipatedspeech that left the possibility of a interest rate hike inDecember open to interpretation.

U.S. Treasury yields dipped as Yellen's speech at an annualmeeting of central bankers in Jackson Hole, Wyoming, relievedsome investors who had expected hawkish comments on the economy.

Reforms that followed the 2007 to 2009 crisis hadstrengthened the financial system without impeding economicgrowth, and future changes should be modest, Yellen said inprepared remarks.

"She didn't say anything that the market wanted to knowabout Fed policy," Marc Chandler, chief global currencystrategist at Brown Brothers Harriman & Co.

"It's seen the 10-year yield slip and has seen the dollarweaken. It was not that she said anything bullish for foreigncurrencies; it was that she didn't say anything positive for theU.S.," Chandler said.

MSCI's index of stocks across the globepared some gains to edge up 0.32 percent.

U.S. stocks climbed, though the tech-heavy Nasdaq wasdragged lower by Broadcom Ltd after it reportedresults.

European share markets closed lower, with the pan-regionalFTSEurofirst 300 index slipping 0.05 percent, even asan index of emerging market stocks rose.

"People had hoped for some excitement. The bond market israllying with at least some people thinking (Yellen) would makethe case for more rate hikes to take some steam out of the stockmarket," said Chris Low, chief economist at FTN Financial in NewYork.

Benchmark 10-year U.S. Treasury notes rose 5/32in price, pushing the yield down to 2.1781 percent.

The dollar index fell 0.53 percent, with the euroup 0.64 percent to $1.1873 and the Japanese yen gaining0.27 percent versus the greenback to 109.27 per dollar.

The Dow Jones Industrial Average rose 43.44 points,or 0.2 percent, to 21,826.84. The S&P 500 gained 5.4points, or 0.22 percent, to 2,444.37 and the Nasdaq Compositedropped 4.05 points, or 0.06 percent, to 6,267.28.

All 11 major S&P sectors rose, except for technology. TheS&P 500 and the Dow were on course to snap a two-week losingstreak.

Also helping sentiment on Wall Street was a report that saidU.S. President Donald Trump will turn his attention to hiscampaign promise of implementing tax reform.

National Economic Council Director Gary Cohn told theFinancial Times that starting next week Trump's agenda andcalendar is going to revolve around tax reform.

Mario Draghi, president of the European Central Bank, wasscheduled to speak later in the afternoon at Jackson Hole.

The Atlanta Fed's GDP Now forecast model showed the U.S.economy is on track to grow at a 3.4 percent annualized pace inthe third quarter based on the latest data on industrial output,home sales and durable goods orders.

Oil prices rose as the dollar fell and as the U.S. petroleumindustry braced for Hurricane Harvey, which could become thebiggest storm to hit the U.S. mainland in more than a decade.

U.S. crude rose 0.4 percent to $47.62 per barrel andBrent was last at $52.14, up 0.19 percent on the day.

(Reporting by Herbert Lash; Editing by Bernadette Baum)