Google’s (GOOG) share of the U.S. search market increased to 68.29% in May from 67.9% in April and 65.13% a year ago, according to market research firm Hitwise. Meawhile, Yahoo’s (YHOO) share fell to 19.95% from 20.28% a month ago and 20.89% a year ago. Microsoft (MSFT) didn’t fare much better. Market share for its search service fell to 5.89%, from 6.26% in April and 7.61% a year ago.

Despite their best efforts, Microsoft, Yahoo and Ask.com just can’t seem to narrow, even slightly, Google’s massive lead in online search.