Right on schedule, Nielsen’s provided another look at the U.S. search market, and although absolutely nothing changed at the top – Google’s market share didn’t fluctuate at all between April to May – something interesting did occur last month as Yahoo and Bing gained ground.

Here’s a little bit of historical info in case past stats don’t come straight to mind: ever since Microsoft and Yahoo first announced their partnership, there’s been a fairly steady tradeoff in market share between them.  Which is a bad thing from both companies’ perspectives, since it implies Microsoft’s paying for technology it doesn’t need.

Nielsen’s data covering May indicates the companies each have something to bring to the table, however.

Nielsen determined that Yahoo managed to increase its market share by 0.3 percent on a month-over-month basis, and Bing increased its share by 0.1 percent.  That left the two organizations with market shares of 13.8 percent and 13.0 percent, respectively.

So now Yahoo and Bing are a tiny bit closer to Google (with its market share of 65.1 percent), and have put more distance between them and fourth-place AOL.  (AOL was in fact the big loser in May, getting left with a market share of 2.1 percent after seeing its standing drop 0.4 percent.)

It’ll be very interesting to see if Yahoo and Bing can sustain this growth.  For that matter, even continuing to hold Google back would count as an accomplishment.