Hidden Assets : Residential customers demanding bigger, unseen tank models.

To many affluent suburban residential consumers these days, bigger is better. The same customers who choose maximum sport utility vehicles (SUVs) and prefer to supersize their fast-food meals are ordering underground propane tanks that maximize their on-hand fuel supply and reduce the number of deliveries needed annually.

Underground propane tanks -- considered less unsightly and safer than above ground tanks -- are growing in popularity in affluent areas such as New York's Bridgehampton on Long Island, New Jersey (now the nation's most affluent state), and Washington, D.C. suburbs in rural Maryland. They are also popular in upscale neighborhoods in places including Ohio, Missouri, Florida, Virginia, Michigan, Wisconsin, and Washington state.

The safety aspect is at least partially embodied in NFPA 58, which permits underground propane tanks up to 2,000 gallons water capacity to be as close as 10 feet from the nearest property line. Above ground tanks exceeding 500 gallon are required to be at least 25 feet from the line.

Byron Caffey, assistant director of LP gas safety for the Texas Railroad Commission, notes that there are at least two good reasons for that. One is the danger that a house poses to a tank. "If you had a building that was on fire, it would have less of a danger of impingement upon an underground tank."

Also, tanks set underground are in a milieu that has a more constant temperature -- usually cooler than a Texas tank would be above ground in the summer, and warmer in the winter, thereby enhancing vaporization. In the Lone Star state, underground residential tanks are popular in the hill country of West Austin, and among residents of new, up-scale suburban Dallas neighborhoods.

The Texas Railroad Commission offers marketing materials that propane retailers use to promote undergrounding. One brochure includes color photos of well-landscaped underground installations, with the slogan, "The eyes of Texas are not upon us."

Attractiveness is key for many consumers. Since only the dome is visible, tanks can be incorporated into most landscape designs. Both safety and aesthetic concerns have led some local communities to require buried tanks.

Whatever the reason, manufacturers report growing interest in larger underground tanks. A propane industry study published by the …