Google again led the U.S. core search market in October, but Microsoft Corp.’s (MSFT) bing.com also posted market-share gains, according to market research firm comScore Inc.

The search leader had a 65.4% share in October, posting a 4% month-on-month rise to 9.4 million core searches. Microsoft’s upstart site had a 9.9% share and handled 8% more searches. Both posted half-point gains in share from September, with most of their gains coming out of the hide of Yahoo Inc. (YHOO). Yahoo posted a 0.8-percentage-point decline from the September share to 18%.

The total core search market was up 3% to 14.31 billion queries. Meanwhile, in comScore’s analysis of Web sites where search activity is observed, expanded searches posted a 3% sequential gain to 22 billion. Google again led with 13.51 billion searches, with Yahoo and Microsoft at 2.66 billion and 1.46 billion, respectively.

For friend networking sites, News Corp.’s (NWSA) MySpace sites posted a 4% drop to 472 million search queries, and Facebook had a 14% drop to 331 million. MySpace, like Dow Jones & Co., publisher of this newswire, is owned by News Corp. (NWSA). In e-commerce, Amazon.com Inc. (AMZN) sites were down 2% to 212 million. EBay Inc. (EBAY) search queries fell 1% to 617 million. Privately held Craigslist Inc.’s search queries fell 5% to 594 million.