"likely source" is an acceptable phrase when used in written English.
For example, "Experts identified the likely source of the contamination as an industrial plant near the river."
Russia is the most likely source.
"He sees China as a pretty likely source of that".
The likely source is not atmospheric pollutants, but lab accidents.
Among the newest road-trip planning tools is one from a likely source, AAA.
It came from a less likely source: the Chinese Propaganda Department.
Keeping those things would require financial incentives and the taxpayer would be the most likely source.
Another likely source of pure streams of carbon dioxide are plants that refine natural gas.
Keyworth was named as the likely source of the leak to Dawn Kawamoto.
With its somewhat bland, tan stone facade, the building hardly seems a likely source of controversy.
The most likely source remains Miller, who will be one of the favorites in Sunday's slalom.
The Agriculture Department now says Pilgrim's Pride was a likely source of the summer outbreak.
