BYOB restaurants are a boon to the cost-conscious diners who enjoy drinking wine (or beer) with their meal, but are loath to pay the high markup at restaurants. Although Pittsburgh has an impressive number of BYOB restaurants with wonderful food (Legume, Bona Terra and Vivo come immediately to mind), wine connoisseurs often take advantage of another type of BYO to pair good wine with good food.

Most fine-dining restaurants with their own wine programs allow guests to bring their own wine and pay a corkage fee, essentially a charge for the service of the wine.

Wondering why you haven't heard much about this before? Restaurants see the practice as a courtesy, but most have good reason to continue it. Serious wine drinkers tend to want to eat good food with their own wine. When corkages rise, or restaurants no longer allow the practice, these customers react negatively.

So instead, restaurants have policies, but they keep them fairly quiet, not only because they don't want it to become common practice, but also because there is a delicate etiquette to the practice that is difficult to spell out.

To begin with, a corkage fee at a wine-selling restaurant is not the same as a corkage fee at a BYOB restaurant. At a BYOB restaurant, you are generally paying a nominal price, something like $5 a bottle or $2 a glass, to compensate for the cost of wine glasses and service of un-corking.

At wine-selling restaurants, the fee is usually higher. According to Lettie Teague, a wonderful wine writer whose column appears in Food and Wine Magazine, the national average is about $25 per bottle, but in cities like New York, Las Vegas, and San Francisco, it is not unusual to find corkages of $35 or more.

The fees are higher because many restaurants invest a lot of time and money in training staff, acquiring the finest glasses and buying and cellaring their wine. If guests bring their own, they need to compensate for the aspects of their investment that the guests are benefiting from, and make up for some of the revenue lost.

At Le Pommier, a French bistro on the South Side, the corkage fee is $5 per stem. So, if four people bring a bottle of wine, they're going to pay a corkage of $20. If they bring two bottles, it's $40.

Le Pommier waives the corkage fee on Mondays, typically a slow night in the restaurant industry. It also waives the corkage if the guest also buys a bottle from the list.

House manager Jeremy Carlisle says that on some Mondays everyone brings their own wine, on other Mondays no one does. On other days, he estimates that only about 5 percent of the wine drunk in the restaurant comes from outside, and most of that is from people who regularly come to the restaurant and bring their own bottles.

He agrees with the standard rule of thumb that you shouldn't bring a wine that's on the house list, but that's not really an issue at Le Pommier, because "very few of my wines are available anywhere."

He also agrees that the customer should offer his or her server or the sommelier (whoever is appropriate in the situation) a taste of the wine--not a glass, just a taste.

Mr. Carlisle also made a good point that many diners may not have considered. He worries that people who bring their own wine sometimes undertip servers, who have to do just as much work as if you bought the wine from the restaurant.

Of course, whether to tip a server the usual percentage no matter the price of the wine is a different conversation.

The corkage fee at Downtown's Capital Grille is at the high end for Pittsburgh restaurants -- $25 per bottle. Wine director Chris Amman said very few people bring their own bottles. If a customer calls ahead, he would ask them not to bring a wine on the list. Mr. Ammam and Mr. Carlisle both spoke very much from the perspective of the restaurant -- they have good wine lists so there's really no reason to bring your own wine.

Of course, restaurants have an obvious incentive to discourage this practice. Wine markups have increased in recent years to where threefold is common. While restaurants can cite a lot of good reasons to justify this markup -- restaurants spend a lot of money buying and storing wine, training servers, and selecting good stemware and other wine accessories -- it's hard to overlook the fact that restaurants with serious wine lists are making serious profits from those lists.

Restaurants also have good reason to discourage people from bringing cheap, generic wine to a restaurant just to save a few bucks. It's embarrassing for a high-end restaurant to have mediocre bottles of wine on the tables.

Most people, however, who take advantage of corkage fees are unlikely to bring the cheapest bottle of wine. They simply want to spend more of their money on the wine, rather than the restaurant's markup. There are plenty of bottles of wine that are inexpensive but pair well with food. After all, wines for which restaurants charge $45 may be available to the consumer for as little as $15.

And it's important to point out that not every restaurant has a great list; even if the restaurant has great food, there is a lot of bad wine out there. Also, not everyone has the same taste. Just because a restaurant has a list with some interesting wine doesn't mean that every customer will find a wine he or she loves, at a price he or she can afford.

And as much as restaurants might like us to forget it, bringing your own wine can save you money without sacrificing quality of wine. If you take a $15 bottle to a restaurant with a corkage fee of $15, you're still paying just $30 for a bottle of wine that would have almost certainly cost more if purchased from a restaurant list.

Still, people shouldn't necessarily be so hung up on wine markups, especially here in Pennsylvania where restaurants are going to the trouble of special-ordering a lot of wine that isn't available in State Stores without some extra effort. Does it matter that you paid $40 for a bottle of wine that a restaurant paid $10 for, if you really like the wine and would never have tried it otherwise?

Reason probably lies somewhere in the middle. People who are interested in wine have a good sense of their own tastes. If you enjoy certain types of wines and you feel they are good wines, irrespective of their price, no one should make you feel uncomfortable for wanting to enjoy them at a restaurant that allows you to do so.

Probably the most important rule of bringing your own wine to non-BYOB restaurants is always to call ahead. Since corkage fees and rules are rarely publicized and vaguely spelled out, they often change, and there's nothing more frustrating or more likely to kill an evening than an unexpected (often large) addition to the bill.