It has been involved in the development of oil shale since 2005.

I am a bit too old to work on the oil shale.

The price of oil shale itself, however, has not risen.

In 1924 the power plant was switched to oil shale.

In addition, it produced other chemical products from oil shale.

Of all the power plants fired by oil shale, the largest was in this country.

In the 1970's he worked on the recovery of petroleum from oil shale.

There are more than 30 known occurrences of oil shale.

This mineral is embedded with oil shale in many areas.

It was the first power plant in the world to employ oil shale as its primary fuel.