Wines by the glass are the worst offenders, says Mark Oldman, pictured. Courtesy of Mark Oldman Anyone who's ever dined out knows a glass — or bottle — of wine is a quick way to inflate your bill.

But why can you buy an entire bottle of wine for $15 at a liquor store, while the cheapest option at the local Italian place is a $13 glass of Chianti?

In his book "How to Drink Like a Billionaire," sommelier Mark Oldman writes that a typical restaurant marks up a bottle of wine at least 200%. That bottle of wine purchased for $15 wholesale, then, quickly becomes a $45 bottle of wine, and it may be marked up by as much as 400% — plastering on a $75 price tag.

"The need to cover glassware, staff wages, rent, inventory — the reasons are sundry for why wine is marked up an average of three times or 300 percent over the restaurant's wholesale cost, and sometimes much more than that," Oldman writes. "But to diners, wine pricing in restaurants seems less like money management and more like cash extraction."

Oldman says aside from the costs of running a restaurant, the location and size of the establishment affect the price, as well as whether management thinks the customer will notice: "A restaurant that purchases a bottle for $5 wholesale can mark it up a dizzying 600 percent to $30 without most diners noticing," he writes. But those same diners are much more likely to balk at a 600% markup on a $30 Bordeaux.

And prices of wines by the glass are the most inflated. "Wines by the glass are so marked up that it is practically industry scripture that the cost of the first glass covers what that restaurant paid wholesale for the bottle," he writes. Instead, knowing a typical bottle holds five five-ounce servings, he recommends dividing the price of a bottle by five to figure out how much you're paying for a glass.

To find restaurants that "play fair" with their wine lists, Oldman provides a list of tips, including:

Avoid hotel restaurants. "Catering to business travelers, wedding parties, and other free spenders, hotels often price their wines like they do that hamburger that somehow costs $40 through room service."

Ask about corkage fees. "Is the restaurant's corkage fee for BYO unusually high? If so, then they are probably similarly rapacious when pricing the wine."

Go where the pros go. "Every city has certain restaurants favored by chefs and sommeliers, and these tend to be the ones with more reasonable wine markups. Follow them on social media or use Google to see where they are regulars."

If that last tip appeals to you, Oldman himself is on Instagram and Twitter as @markoldman.