A side-effect of the ongoing restaurant boom in Philadelphia: The price of a liquor license is skyrocketing.

Licenses that two years ago sold for $85,000 are now priced at nearly $120,000, according to lawyers who specialize in the transactions.

Compare that to 2002, when they sold for $35,000.

Many restaurateurs consider a liquor license to be essential, as alcohol sales are far more profitable than food. Liquor licenses are governed by the state Liquor Control Board but are sold by restaurateurs on the open market through lawyers or brokers, and that's where basic economics comes in.

There are simply no licenses available, according to three local lawyers who specialize in liquor licenses.

In Philadelphia, an R license cost $15,000 to $18,000 in the 1970s and early 1980s. The price rose to nearly $28,000 in the early 1990s, and reached $35,000 in 2002 before making a steady climb over the last decade. As recently as fall 2012, licenses fetched between $60,000 and $65,000.

Attorney Paul Herron of Kelly & Herron said that years ago, Philadelphia's numerous corner bars were a steady source of licenses, since they can be transferred from person to person and from place to place within a county.

But "the neighborhood bars are largely gone," Herron said. Many of these licenses have already been repurposed in Center City and in the high-growth neighborhoods such as East Passyunk and Fishtown. But some of the remaining licenses have been revoked because operators of these establishments failed to pay state taxes. Once a license is revoked, it cannot be reinstated, trimming supply.

One example, according to state records: The license for the now-defunct Farmers Cabinet in Center City.

The trend won't price people out of the market, Herron said. Restauraturs will simply dig deeper. Licenses are an asset, and he does not see the prices dropping any time soon.

The number of licenses for each municipality was set after Prohibition by the legislature, which based it on population.

Prices in Pennsylvania's suburban counties are dramatically higher, with most at $200,000 or higher.