Perusing online wine ratings last month, I came across a review of a wine in Steven Tanzer’s International Wine Cellar that was more than a mere rave. The wine was Domaine Roger Perrin’s 2003 Chateauneuf-du-Pape Reserve, and Mr. Tanzer wrote that this “suave, entrancing wine is at the top of my ‘must-buy’ list from 2003.” Since I respect Mr. Tanzer’s expertise, I decided that this wine would also be a personal “must buy.”

And so I logged on to wine-searcher.com, a Web site that tracks inventories of 7,700 merchants worldwide. It listed a dozen “hits” for Perrin Chateauneufdu-Pape, including one at a shop just a few blocks away from my front door, priced at $74.99. But the wine was also offered at the Big Y, a retailer in Northampton, Mass., for only $47.95. As it happens, family connections take me often to Northampton, and I always try to stop by the Big Y. Five minutes after seeing Mr. Tanzer’s review, my online purchase of three bottles was confirmed. Those bottles will remain in the Big Y’s cool storage cellar until autumn. And since Massachusetts does not charge sales tax on wine, the savings on those three bottles, compared to the price with tax at my neighborhood shop, exceeded $90 — enough to buy an extra couple of worthy bottles.

Once, the shelves of my home office were dominated by piles of wine periodicals. No more. But as my experience with the Perrin shows, the Web is drastically changing many wine-buying decisions: It’s where I first read about the Perrin, where I did my comparison shopping, and where I bought it. Below are the four wine Web sites I find most useful. Alas, they aren’t free, but they have proven their worth many times over in the fluid and confusing arena of wine shopping.

EROBERTPARKER.COM The core of “eBob,” as Robert Parker’s fans fondly call this site, is a database of more than 80,000 wine ratings by the world’s most influential critic. Even without the ratings, however, its wide-ranging extra features would make the site worthwhile. In Hedonist’s Gazette, for example, Mr. Parker’s play-by-play of marathon wine dinners are so vivid (check out the eight-course, 12-wine affair on June 6) that I sometimes feel like I need an Alka-Seltzer halfway through reading. EBob also includes daily wine news updates, smart buys from a shopping service called PriceAlert, and links to articles by top food and wine journalists including Alan Richman and Lettie Teague. There’s also a vast chat room echoing with impassioned voices on wine, food, and travel. In all, a world in a Web site.

Subscriptions: $99 a year, or $29 for 90 days at erobertparker.com. “Parker in Your Palm,” for mobile consults of the Parker wine database on Palm Pilots, is available in two formats at $29.95 and $49.95 annually.

STEVEN TANZER’S INTERNATIONAL WINE CELLAR (wineaccess.com/expert/tanzer) Though this Web site doesn’t have all the features of eBob, it does have, in Mr. Tanzer, a wine critic whose palate of wine descriptors is unrivaled. In the “utterly seductive” aromas of that Perrin Chateauneuf-du-Pape 2003 I bought, for example, he found “ripe cherry, blackberry, kirsch, pungent floral oils, fresh meat, and candied red licorice.”And that’s before he’s even tasted it! Some would question whether Mr. Tanzer can actually pick up so many aromatics. My conviction, after over a decade of reading him, is that he’s simply got more olfactory receptors than normal humans, and that he’s found a calling that allows him to use them to the fullest.The site’s wine ratings are voluminous and easily searched. The Wine Access feature allows searching of the inventories of more than 150 wine shops. There’s also a wine chat room in which the colloquy is as spirited as it is on eBob.

Subscriptions: $80 a year or $40 for six months.

WINESPECTATOR.COM A databank of more than 160,000 wine ratings culled from issues of the world’s largest circulation wine magazine going back to 1994 anchors this eclectic site. It also has a vast repository of the magazine’s articles. My search for stories mentioning California winemaking guru Helen Turley, for example, yielded 215 hits (although some were duplicates). A gossipy bi-weekly feature called Unfiltered, the closest thing in the wine world to Page Six, covers such spicy subjects as a porn star’s debut as wine producer and what wine Pamela Anderson drank to calm her nerved before marrying Kid Rock. I have a personal addiction to a feature called “What Wine is This?” Based on a careful reading of an actual Spectator tasting note, with the name of the wine withheld, one is presented with a series of multiple choice questions. If answered correctly, they will lead to identification of the wine’s variety, country or region of origin, age, and appellation. A point-by-point explanation of the correct answers can help to sharpen one’s wine ID skills — and coming up with the answer on one’s own is good for the wine ego. The site also includes a directory of 3600 restaurants with “Awards of Excellence” from Wine Spectator.

Subscriptions: $49.95 annually or $7.95 monthly.

WINE-SEARCHER.COM From its headquarters in New Zealand, this Web site keeps track of what’s on the shelves at serious merchants worldwide. New York is home to 229 of the listed shops. Inventories are updated twice weekly. A free version shows listings only at shops that pay Wine-Searcher to be listed, while the “Pro-Version” includes additional shops that are often lowest-priced. Checking on the excellent Woop Woop 2005 Shiraz, South Australia, I found 35 sources in New York City, ranging in price from $7.99 at PJ Wines to $13.99 at Sussex Wines. If you have PJ deliver a few cases of Woop Woop, rather than buying it at the highest priced shop, you’ll pocket a nice piece of change. Looking for an ultimate rarity? How about Romanee-Conti 1875, Burgundy’s greatest wine from a vintage that is apparently still alive in the bottle. Wine-Searcher has sources for this wine in Switzerland, Germany, and England, priced between $12,917 and $15,831.

Subscriptions: $29.95 annually for the Pro-Version.