In the world of real estate brokerage, the most valuable commodity of all is a listing.

This is not to say that buyer brokerage agreements lack value, but it's tough to decorate a web site or newspaper ad with spiffy photos of would-be purchasers. Buyers are buyers but listings are visible inventory, and for marketing purposes there is a difference.

All of which gets us to the online value of listings. We know that listings have value to brokers, but what is their value to online sites?

There is the argument that major realty sites cannot exist without listings, and thus such sites should pay brokers or MLS systems for the right to show listing inventory. For the past several years, MLS systems have been able to get from $1 to $3 per listing per month, a tidy addition to the bottom line.

But such numbers are likely to change and for this reason: To this point the purchase of listings has been subsidized by the willingness of investors to fund such sites. Once such funding ends or is reduced, sites will be forced to pay for listings from earnings. The catch, of course, is that many online sites can hardly pay for paper clips, much less anything else.

Imagine that at any moment there are 1.5 million homes for sale nationwide. To get 90 percent coverage, a site would need to acquire 1.35 million listings. At $1 to $3 per month per listing, the cost to show such inventory would range from $1.35 to $4.05 million a month, or $16.2 to $48.6 million a year.

In the great days of the dot-com boom -- say two or three years ago -- raising millions of dollars was fairly simple: You showed up at any nearby venture capitalist for a private placement or sold stock with an IPO and picked up a check.

Dollars were easy to find because the real money was not in the business being underwritten, it was in the valuation of the stock. If a company netted $25 million a year selling widgets online, that's great. If shareholder equity increased by $600 million in a 12-month period, that's even better.

Alas, few online ventures ever made a dime, so the money raised on Wall Street and through private placements has been used for operating funds with the hope that at some point the start-up would generate real cashflow. And while AOL and eBay prove that it's possible for online ventures to be profitable, such companies are hardly typical.

None of this is a minor matter for local MLS systems. For the past several years many have reaped substantial payments from major online sites, but with a decline in Wall Street attention such payments are now likely to be diminished or ended entirely.

Ask this question: How can it be any other way? On the basis of their own revenues, online sites simply do not have the dollars necessary to pay out huge sums of money for listings -- or much else.

In the usual case, if a buyer can't purchase your goods, you say "great" and find another buyer. But in the case of online sites, the situation is different.

First, buyers that were in the mix a year ago purchasing MLS listings are falling away and new ones are not emerging.

Second, many MLS systems will continue to supply listing data whether paid or not. Why? Because major sites are useful to brokers and many realty professionals like the exposure they receive online.

We are about to see the emergence of a new reality -- and for many MLS systems that reality will mean fewer dollars in the till.

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