Speculatively-built office buildings are sprouting around the beltway so fast that you think nobody could count them.

But somebody has, a New Jersey entrepreneur named Robert Black, who's just published the first directory of office space in the Washington market.

"Black's Guide" is patterned after similiar publications that Robert Black and his brother James -- a former commercial real estate broker -- have published for the Netw York and Philadelphia markets.

It's strictly a suburban manual, stopping at the District line, but it lists 400 office buildings in the Maryland and Virginia counties surrounding Washington.

Need offices near Tysons Corner? Black lists a couple of pages of them, with rents ranging from $7 to $12 per square foot, providing such vital statistics as size, rentals and the name and phone number of the rental agent.

For newcomers to the office rental game, the book explains the difference between net and gross rentals, tackling tricky questions about who for what and how much.

By Black's count, there are 424 buildings with 34 million square feet of space in the suburbs. He estimates the vacancy rate at 18 percent -- just over 6 million square feet -- but that includes a number of buildings that aren't yet ready for occupancy.

Available from the publishers in Red Bank, N.J., "Black's Guide" is also being distributed by most of the county and local development agencies in the Washington suburbs. It's a good introduction to the local market for businesses considering moving to Washington and a plus for development efforts.

Black has put out a useful book for office seekers, but the omission of downtown Washington buildings is a major shortcoming. Black insists his specialty is suburban office markets, but downtown is rapidly becoming the hottest office market in the whole metro area.

Next time, Rob, don't leave out Washington.