US public corporations spent an average of just over $1 million on board compensation last year, according to a study of more than 3,000 American companies by The Corporate Library.

These payments included the total of director cash payments, equity awards, and changes in value of pensions and non-qualified deferred compensation amounts.

Almost one-third (32 percent) of the firms in the study paid less than $500,000 in compensation to the full board last year.

At the other extreme, nine companies paid more than $2 million in cash director fees in 2006, including American International Group, Honeywell International, and Northrop Grumman.

One company - Valero Energy - spent more than $30 million on its board of directors, with most of that pay going to a single director, William Greehey. The amount of total board compensation varied based on market capitalisation.

"The findings show that, with the exception of a few outliers, most companies are not spending an unreasonable amount on their boards," said the report's author, senior research associate Annalisa Barrett.

The study also found that, while the practice is very unusual, six companies offered their full board a cash bonus based on company performance. On the other hand, the practice of establishing stock ownership guidelines for directors is on the rise.

For the Stand & Poor's 1500 (S&P), the prevalence of ownership guidelines has increased from 29 percent in 2005 to 46 percent in 2007. The study provides a detailed analysis of the stock ownership guidelines in place at S&P 500 companies.