March 10 (Bloomberg) -- March 10 (Bloomberg) -- Investors are the most bullish on the dollar since the collapse of Lehman Brothers Holdings Inc. on speculation the U.S. economy will expand at a faster pace than in Europe and Japan, a survey of Bloomberg users showed.

 The world’s reserve currency will rise over the next six months, according to respondents in the Bloomberg Professional Global Confidence Index. Sentiment toward the U.S. economy rose among the 1,612 participants in the survey, even as the outlook for global growth fell for a second consecutive month.

The dollar strengthened this month to the most since May against the euro on concern Greece’s struggles to close the biggest deficit in the European Union as a percentage of gross domestic product will weigh on the region. The Federal Reserve will raise interest rates before the European Central Bank and Bank of Japan, according to the median estimate of more than 30 economists surveyed by Bloomberg.

“Growth differentials and interest-rate differentials, and the fact that the U.S. is so far doing quite well compared with the euro-zone” have benefited the dollar, said Meg Browne, a vice president of foreign-exchange research at Brown Brothers Harriman & Co. in New York and a survey participant. Greece has been “one of the drivers of dollar strength. There are a number of reasons why longer-term, we think the dollar will strengthen,” she said.