Colvill tells GlobeSt. that negotiations with Southern Union began six months ago when the company made it known that it had outgrown its existing space and was looking for a new home. The gas company considered buildings in downtown, Greenway Plaza and the Galleria submarkets.

Galleria Tower II competed with at least four other buildings, according to Colvill. The 1970s-era building is connected to The Galleria, a mixed-use project comprised of three office towers totaling 1.1 million square feet, two hotels, 2.4 million square feet of retail space and more than 35 restaurants.

Colvill says Southern Union was attracted to the building’s immediate access to the Galleria's retail, restaurants and hotels. These amenities, coupled with the building’s large block of space, were the deciding factor, according to Eric D. Herschmann, vice chairman, president and COO of Southern Union.

Southern Union, which will get top-of-the-building signage with its new lease, brings yet another credit tenant to the Galleria complex. It will join other Galleria complex tenants including: Air Liquide America, Wachovia Securities, Morgan Stanley, Merrill Lynch, UBS Financial Services and Citicorp.

With the Southern Union lease signed, Chicago-based Walton Street Capital has decided now is the time to sell the three Galleria Office Towers. The owner tapped HFF’s local office to market the properties, which were listed without an asking price.

Local experts estimate the iconic buildings will sell for about $175 per square foot. Using those metrics, the Galleria Office Towers will trade for $193 million.