Each company says it needs 10 or 15 percent to prove truly viable.

This proved commercially viable during most of the 1950s.

The extension did not prove viable and the previous length of operation was restored for the 2011/2012 season.

The technology involved had not been proved viable at a commercial scale.

To date, this technology has not proven commercially viable.

Satellite service will drive those markets' if it can prove viable.

Neither strategy proved viable and the entire process was one disaster after another.

If the wells prove viable - a risky assumption in the energy business - then the life of the contract might be worth $1.7 billion.

"But in the end, the real issue is whether it will ever prove commercially viable, and for now, that seems unlikely."

In the industry many questioned whether the show would prove viable.