DENVER -- The Colorado Rockies' method of storing baseballs is fast growing from a curiosity to standard operating procedure in the Majors.

Since 2002, the Rockies have kept baseballs in an atmosphere-controlled climate, known locally as "the humidor," to keep them from shrinking, hardening and losing friction in Colorado's unique environment. Major League Baseball stopped short of mandating all teams adopt such an apparatus, but the move toward standardization will continue in 2007.

All 30 clubs will be keeping their baseballs in temperature-controlled settings. In another move toward ensuring that balls stay at specifications set by manufacturer Rawlings, Major League Baseball has adopted a shelf-life rule, MLB executive vice president, baseball operations Jimmie Lee Solomon said Thursday.

"We did send out a directive that teams are to use current year-purchased balls, not balls from previous years -- they may use those in batting practice, but not in games," Solomon said.

As for storage, Solomon said some clubs have humidity controls for the area where balls are stored, but he did not know how many.

Much of the focus on baseball storage is on the Rockies, who began operating the humidor in 2002. Before then, runs and home runs were at an off-the-charts pace at Coors Field. The prevailing theory was that the increase was due, partly at least, to the mile-high dry climate of Coors Field in Denver.

Whenever there is a run of high-scoring games, the Rockies are questioned about how they're operating the humidor, but Solomon said what the Rockies are doing "will be the industry standard in the not-too-distant future."

As has been the case for the last five seasons, the Rockies must file weekly reports with Major League Baseball, and MLB operations will travel to Coors for periodic checks. Solomon said the Rockies are monitored more than any other club.

Solomon called the monitoring of a climate's effects on baseballs, and in turn how the ball performs in games, "an emerging science." But the eventual goal is to make sure that the baseball in all venues stays at Rawlings' specifications, presumably with all teams storing them in a standard chamber.

"It's going to take time -- it's not a cheap apparatus," Solomon said.

The one at Coors reportedly cost $15,000, not counting the cost of operating it and filing paperwork.