Another situation in which a trading halt might occur is when the exchange is uncertain "whether the security continues to meet the market's listing standards."

But because the exchange has much stricter listing standards, it cannot compete with Nasdaq for smaller companies.

Q. The Nasdaq stock market has announced plans to consider reviewing its listing standards.

A possible force for change could come from the stock exchanges, in a new listing standard.

Trying to impose a new listing standard on an exchange can involve a long, contentious review process.

The Philadelphia exchange's listing standards look reassuring on paper.

Its listing standards are tougher than those of other markets, and its trading costs are lower.

And Skybox does not meet the listing standards of any national exchange.

The idea was that the stringent listing standards imposed by exchanges would provide adequate protection for investors.

For this reason, we began a review of our listing standards several months ago.