Salt served as a valuable source of income for the French king.

The industry provides a very valuable source of foreign exchange.

These works are the most important and valuable sources for Scottish history in the late 12th century.

The king said the woman would be a valuable source of information on the Iraqi terror group she had joined.

It is important to talk to employees, as they are a valuable source of information and advice.

All of these may be a valuable source for recruitment.

Thus, he became a valuable source for an older tradition.

And if those were purchased on the black market, someone has a very valuable source.

The work is a very valuable source for colonial historians.

They are a valuable source for our knowledge of Luther.