* Graphic: World FX rates in 2017 tmsnrt.rs/2egbfVh
* Global Assets in 2017 reut.rs/2ne9sjH
* Wall Street dips, dollar flat
* MSCI world index on track for more than 6 pct gain for quarter
* Oil has worst quarter since 2015 (Updates prices, adds oil market closes)
By Caroline Valetkevitch
NEW YORK, March 31 (Reuters) - An index of world stocks dipped on Friday as investors locked in a quarterly gain that has given equities their best start to a year since 2012, while oil prices finished their worst quarter since 2015.
U.S. stock indexes were mostly lower in afternoon trading. The S&P 500 was on track to gain about 6 percent for the first quarter, its biggest quarterly gain since 2013.
Emerging market equities fell the most, with the MSCI emerging markets index down 0.9 percent on Friday. MSCI's EM stocks index is up 12.5 percent on a dollar-adjusted basis. reut.rs/2ne9sjH
Equities saw profit-taking as traders squared up for the quarter. There was remaining nervousness over South Africa's sacking of its respected finance minister, which sent the rand tumbling again.
World stocks as measured by the MSCI world equity index were down 0.3 percent on Friday but up 6.6 percent for the quarter so far.
U.S. stock investors are now looking to the upcoming quarterly earnings season to justify pricy valuations.
The S&P 500 index is trading at about 18 times earnings estimates for the next 12 months, compared to its long-term average of 15.
"Valuations are as stretched as they ever get," said Bruce Bittles, chief investment strategist at Robert W. Baird & Co in Nashville. "Certainly that's cause for concern if earnings don't grow the way they are anticipated to grow."
The Dow Jones Industrial Average was down 54.43 points, or 0.26 percent, to 20,674.06, the S&P 500 had lost 2.85 points, or 0.12 percent, to 2,365.21 and the Nasdaq Composite had added 3.00 points, or 0.05 percent, to 5,917.34.
In commondities, U.S. oil prices ended slightly higher on the day but had their worst quarterly decline since 2015.
Brent oil settled down 13 cents at $52.83, while U.S. crude futures rose 25 cents to settle at $50.60.
U.S. Treasury debt yields were mostly lower after New York Federal Reserve Bank President William Dudley said the central bank was not in a huge rush to tighten monetary policy since the economy is not overheating.
Ten-year notes were up 2/32 in price to yield 2.410 percent, compared with 2.418 percent on Thursday.
In an interview with Bloomberg TV, Dudley, a permanent voter on the Federal Open Market Committee and a known supporter of low interest rates, said a couple more rate increases in 2017 seem reasonable but that there is no great urgency.
The dollar index was near flat after Dudley's comments and following uninspiring data on the U.S. economy. Over the quarter the greenback has fallen 1.8 percent, its worst showing in a year, on doubts that U.S. President Donald Trump was not prioritizing - and did not have the necessary power to push through Congress - the economic reforms that had driven the dollar to 14-year highs at the start of the year.
Next week promises to be an interesting start to the second quarter.
Trump and Chinese President Xi Jinping will meet in Florida and the U.S. president has set the tone for a tense few days by tweeting that Washington could no longer tolerate massive trade deficits and job losses.
For Reuters Live Markets blog on European and UK stock markets see reuters://realtime/verb=Open/url=http://emea1.apps.cp.extranet.thomsonreuters.biz/cms/?pageId=livemarkets
Additional reporting by Noel Randewich in San Francisco, Marc Jones in London; Editing by Alistair Bell and Chizu Nomiyama