Google's leadership on the Web stems partly from its powerful data centers, which allow it to provide lightning-fast search results while keeping energy costs to a minimum. The company has been mostly secretive about what goes on inside these giant computing factories, but on Wednesday it offered a peek at what it has been able to achieve -- on the energy side at least.

Google has published results from internal studies showing that its data centers are "the most efficient in the world," according to a blog post from Urs Hölzle, its senior vice president of operations. While some of what it does, like designing its own servers, isn't practical for most businesses, other tricks could be replicated by other companies, albeit for an upfront capital cost.

Its announcement coincides with a speech about energy that CEO Eric Schmidt is due to give Wednesday evening in San Francisco. Schmidt will argue that the US can reduce its oil dependency by drilling for "natural and clean geothermal energy" and making a "bold move" into solar and wind power, according to the event's agenda.

Google uses a metric called PUE, or Power Usage Effectiveness, to measure its data center efficiency. It gives a ratio of the total power consumed by a data center to the power consumed by the IT equipment used in the facility. For example, a PUE of 2.0 indicates that for every watt that directly powers the IT equipment, an additional watt is used to cool and distribute power to that IT equipment.

In a report to the US Congress in 2006, the Environmental Protection Agency estimated that the typical enterprise data center had a PUE of 2.0 or higher. It also forecast that by 2011, data centers employing "state of the art" techniques such as liquid cooling could reduce their PUEs to 1.2.

Google said Wednesday that it has achieved that PUE as the average across all of its data centers, and that one of them operates with a PUE of 1.13. "Today we are operating what we believe to be the world's most efficient data centers," Hölzle wrote.

That's no small claim given that many of its competitors are also experimenting with data center designs to improve efficiency. Microsoft has been packing servers into shipping containers, creating a closed environment that allows it to manage cooling more efficiently. The company said recently it had achieved a PUE of 1.3 in one of these containers. They are not widely in use yet, but Microsoft plans to put more than 200 of them at a new data center in Chicago.