The greenest retailer in the U.S. is Wal-Mart? Known for its superstores, stringent supply-chain economies and “always low prices,” Wal-Mart Stores Inc. is considered by many the most influential retailer in the world. But few associate the company's 1,000-plus U.S. stores with sustainability — even as the mega-retailer has exhaustively tested green initiatives in experimental stores for the past 14 years.

That is, until recently. Wal-Mart's ambitious goal of reducing energy costs and greenhouse gas emissions in new stores by 30% over the next four years — and by 20% in existing stores over the next seven years — may actually be surpassed, says Charles Zimmerman, Wal-Mart's vice president of prototype and new format design.

What's more, the retailer is taking the unprecedented step of sharing green technology with competing retailers. It invited Publix, Costco, Target, Food Lion and like retailers to an environmental products demonstration at a Sam's Club in Savannah in late 2006. Since then, vendors have been directed to share green designs specifically developed for Wal-Mart with other interested retailers.

In January, Zimmerman delivered sustainability presentations to Best Buy, Office Depot and Kohl's — and to the Pentagon — in the course of just one week. “It's not just retail we're talking about here,” he says. “The scenario we find ourselves in with energy and global warming calls for everyone to get on board.”

Some of Wal-Mart's earliest green measures include the installation of reflective “cool” roofing and skylights for daylight harvesting, and the use of low-heat light emitting diodes (LED) lighting. All showed a payback on investment in less than two years, says Zimmerman.

Newer experimental stores located in McKinney, Texas and Aurora, Colo. have yielded a fresh batch of green gadgets, including customer-triggered motion sensors that light aisles and coolers on an as-needed basis during non-peak hours. Bathrooms with low-flow fixtures such as faucets and waterless urinals combine to cut water bills nearly in half. Taken alone, some green measures may only save the company a few hundred thousand dollars annually, but in the aggregate they save tens of millions.

Rainwater harvesting and construction debris recycling are currently being tested. By 2015, the company plans to double its fleet's fuel efficiency by using more efficient truck designs and hybrid diesel engines. Currently, Wal-Mart's private fleet of 7,200 tractors and 44,000 trailers log 900 million miles a year, making 1.8 million stores deliveries.

“These are huge infrastructural decisions that come from years of research,” says Jeffrey Grossberg, spokesman for Chicago-based Skysite Properties, a consortium of real estate investors and professionals who focus on sustainable properties. “Plus, they're not hoarding this technology. They want to drive down costs and help increase the demand for these products.”

On the consumer side of green, Wal-Mart hopes to sell 100 million compact fluorescent light bulbs at its Wal-Mart and Sam's Club stores by the end of this year. The product uses up to 75% less energy than traditional bulbs. Zimmerman says Wal-Mart is following the lead of its chairman, Lee Scott, who last year said the retailer would continue to pursue green initiatives with the same tenacity that it uses to squeeze operating costs.