So I've just read a report with: "the likeliest outcome is...". It called my attention, I would have used "the most likely outcome is...", but then I "googled" and found lots of articles and even dictionaries with the likeliest form. Is it correct?
Google is not a Grammar Site. It will pick up whatever matches the search string you give it. It may or may not be correct.
When in doubt, please consult the dictionary.