These two words strike dread -- not to mention resentment -- in the heart of a solo traveler. Consider for a moment the cost of a superior ocean-view room on a Royal Caribbean International seven-night Alaska cruise. For two adults, it's $1,539 each. For a single traveler, the cost is $2,843 -- an additional $1,304.
Single supplement? Or single penalty?
Royal Caribbean is by no means alone. Supplements are a widespread industry practice in both the cruise and packaged tour industries. Travel companies say that these surcharges (which are generally anywhere from 10 to 100 percent or more of the standard rate) are justified because most accommodations, whether in a hotel or on a ship, are priced for double occupancy.
"To sell that stateroom to only one person," said H.J. Harrison Liu, a spokesman for Royal Caribbean, "that wouldn't necessarily make business sense for us."
Solo travelers, as one might imagine, tend to have a different view of supplements.
"It's the bane of the single person's travel existence," said Bella DePaulo, a visiting professor of psychology at the University of California, Santa Barbara, who studies what she calls "singlism," or the ways in which single people are stereotyped and discriminated against.
One experienced solo traveler from New York, Arlene Rosenberg, decried single supplements and in an email asked me how to skirt them.
"I'm really missing out on a lot of travel opportunities because of this," she said.
Supplements have been around for decades, but with each year they become more out of sync with the nation's demographics as the United States grows increasingly single. According to figures released last year by the Census Bureau, there were 102 million unmarried people 18 and older in America in 2011 -- more than 44 percent of adult residents. That's up from 92 million in 2006, which was 42 percent of residents 18 and older. It won't be long before half of the country is unmarried.
Of course, many unmarried people live with a partner, so not all of them are traveling solo; yet married people aren't all traveling in pairs either. About 12 percent of U.S. adults, married or unmarried, plan to travel solo this year, up significantly from 7 percent last year, according to the American Express Spending & Saving Tracker. And if companies make it more affordable for people to travel on their own -- by dropping supplements and offering deals to solo travelers the way they offer deals to couples and families -- that number might climb even higher.
A number of tour companies -- including Rick Steves' Europe, Backroads and G Adventures -- offer a halfway measure: They will waive the supplement if solo travelers agree to be matched with a roommate. In some cases, if the travel company cannot find you a roommate, you get the room to yourself. Singles travel companies like AllSinglestravel.com offer roommate matching with that guarantee. No matter what, be sure to read the fine print. For instance, SinglesCruise.com notes that it "accepts no responsibility for roommate matching incompatibility such as sleep patterns, snoring, noise or age differences."
Those who want to select their own cruise buddy can try sites like CruiseMates.com, which has a message board where users can post roommate requests.
It's nice to have these options, but for many solo travelers, roommates are something they left behind in college
Ms. DePaulo thinks charging single supplements is ultimately a silly business decision. If travel companies drop the surcharges, they might lose money in the short term, but in the long run they would gain the loyalty of millions of solo travelers.
There are a handful of companies that in the past few years have been willing to do just that by waiving some supplement fees (not just lowering them) and by dedicating a portion of their websites to solo travel. Consider this the first of what I hope will be a growing list of solo-friendly cruise lines and tour companies. Intrepid solo travelers, this one's for you.
Avalon Waterways: One way to avoid single supplements on cruises is to book far in advance, a month or so before New Year's Day or shortly after. For travelers who book their 2013 cruises early, this river and small-ship cruise line dropped the single supplement on a number of departures in Europe, including Magnificent Europe from Budapest to Amsterdam (15 days starting at $4,499 for a single during a recent search) and Paris to Normandy's Landing Beaches (eight days starting at $2,849). Information: Avalonwaterways.com.
Grand Circle Cruise Line: Over the past few years this company, which caters to baby boomers, has had an increase in the number of solo travelers (particularly women), prompting it to address their needs. That meant training guides on how to make solo travelers feel included in all activities, as well as doing away with single supplements on its new small-ship cruises to Myanmar, the French and Italian Rivieras, Turkey and Greece. Information: www.gct.com.
International Expeditions: This nature company has waived supplement fees on select cabins on all of its 2013 Amazon (from $3,898 until July and $4,398 after) and Galapagos (from $5,098) small-ship cruises. Information: ietravel.com.
Norwegian Cruise Line: Norwegian was voted best cruise line for solo travelers last year by readers of Porthole Cruise Magazine. Its Epic has 128 studio staterooms designed specifically for solo travelers. Information: ncl.com.
Vacations to Go: This travel agency offers discounted single supplements for an array of cruise lines like Silversea, Crystal and Paul Gauguin. To find solo travel deals, visit Vacationstogo.com (albeit not the easiest site to navigate) and select "singles discounts" from the column on the left side of the page.
Abercrombie & Kent: "Solo savings," a nascent category of departures to popular destinations such as Egypt, Kenya and Tanzania with this luxury tour company either have no single supplement or are reduced by up to 75 percent. Information: abercrombiekent.com.
Overseas Adventure Travel: Owned by Grand Circle Corp. (the parent company of Grand Circle Cruise Line), this company has no single supplements for any land or small-ship adventures, including the land tour Ultimate Africa: Botswana, Zambia & Zimbabwe Safari (from $5,820) and Ancient Kingdoms: Thailand, Laos, Vietnam & Cambodia (from $3,995). Information: oattravel.com.
Tauck: Founded in 1925, this tour company has dropped the single supplement from Category 1 cabins on all of its 2013 European river cruises, like the 12-day Blue Danube tour, from $4,490. And on certain land tours in Asia, Latin America and Europe, the company offers "solo traveler savings," such as $600 off the regular rates of its popular India tour -- but the trip still costs solo travelers a few thousand dollars more. Tauck does get points for its website, which has a solo traveler forum where you can get answers to questions like "Would I feel comfortable by myself?" Information: tauck.com.
A last bit of advice: Think globally. To avoid supplements and roommates, consider traveling with a company based overseas, like Mercury Direct in London, which has no single supplements for tours of spots as varied as Sri Lanka, Cyprus and Egypt. And the Majestic Line, a U.K.-based cruise company, reserves two cabins for solo travelers on each of its small ships at no additional cost. Information: mercury-direct.co.uk and .