Here's how the top five scored:

-- Google's share grew to 59.2 percent in February from 58.5 percent in January.

-- Yahoo's share shrunk to 21.6 percent from 22.2 percent.
-- Microsoft's was down to 9.6 percent from 9.8 percent.
-- AOL was unchanged at 4.9 percent.
-- Ask.com grew slightly to 4.5 percent, from 4.6 percent.

Online market share data is being watched more closely in light of Microsoft's proposed acquisition of Yahoo. Yahoo Tuesday made public an optimistic financial outlook that relies, in part, on its search advertising revenue growing at least at pace with the market, and its video and display advertising growing faster than the market.

Some observers were skeptical of Yahoo's outlook -- which differed materially from that of several leading Wall Street analysts and looked to many like a justification for its rejection of Microsoft's acquisition offer -- given the economic slowdown stemming from the credit crisis.

Cowen and Company analysts wrote in a note to investors that Yahoo's projections miss "the potential impact of a weakening economy on the display ad market; the likelihood of continued search query share
gains by Google; and the possibility of declining user engagement outside of search."

Citi Investment Research analysts, who have access to more data than comScore's releases broadly, noted that in addition to a month-over-month decline in the total volume of U.S. Internet searches, growth is slowing year over year. Total searches in February grew 15 percent compared with a year earlier. In January, year-over-year growth was 23 percent. In the fourth quarter of 2007, growth was 20 percent.

Citi analysts chalked up the deceleration to the law of large numbers and maturity in the PC search business, rather than macroeconomic conditions.

(Both analyst notes were distributed to reporters by Joele Frank, a PR firm working with Microsoft in its bid for Yahoo.)