Jairo Riveros made eight trips to Europe last year, and had to convert currency each time he crossed from one country to another.

Next month, the New York-based manager of student exchange programs will have to do it only once. Calculating housing and transportation costs for students from different nations should be a snap, too.

As the European Union verges on its historic currency switch, the group most potentially confused - foreign travelers - also stands to gain the most.

Once the new notes and coins start circulating Jan. 1 in the 12-nation euro zone, travelers can save the hassle and cost of changing money multiple times, avoiding commissions of up to 8 percent or more. It'll be easier to comparison shop from country to country for everything from car rentals to wool shawls. Pockets will no longer bulge with francs from France, guilders from the Netherlands and lire from Italy.

``The bottom line is short-term confusion, long-term gain for everybody,'' said John Murray, president of ETM Travel Group, a Westport, Conn., tour operator that sends about 7,000 American tourists to Europe a year.

At first, travelers should expect longer lines at foreign exchange outlets and some retail shops, which will handle both euros and outgoing local currencies during a phase-in period of up to Feb. 28, depending on the nation. And some overseas ATM machines may not be equipped to dispense euros right away.

Shoppers could pay more for some items, as stores round up prices when converting local currencies to the nearest euro decimal. It may be tough for tourists unfamiliar with European costs to figure how much more they're paying.

``It's important that you check your change,'' said Nancy Muller, a spokeswoman for American Express, which operates 380 foreign exchange bureaus in the 12 nations adopting the euro.

To avoid long lines abroad during the transition period - and to make sure you get what you pay for - experts recommend you use a credit card whenever possible.

For small purchases like gelato in Florence or espresso in Paris, you'll want to have euros on hand. So you don't wait in line for money, it's prudent to buy a few hundred dollars worth in advance from a foreign exchange bureau in the United States.

American Express and Thomas Cook, operators of major foreign exchange bureaus here, said they'll start selling euros from outlets in the United States the first week of January. Citibank, owned by financial services giant Citigroup, said it will make euros available from its 446 U.S. branches also at that time.

To supplement pocket change, some vacationers plan to empty out their dresser drawers of European currencies hoarded as souvenirs from previous trips.

``I think I still have some francs left over from last year, and I will take them - less than $100,'' said Elsa Montemayor of San Antonio, who is returning to Paris on Jan. 2 for a 10-day vacation with her husband and two friends.

Outgoing currencies will be accepted until Feb. 28 by businesses in most of the euro nations, including Germany, Italy, Greece and Spain. The exceptions are the Netherlands, until Jan. 27; Ireland, until Feb. 9; and France, until Feb. 17.

Commercial banks will accept local currencies for many months after.

Britain, Sweden and Denmark are the only EU members not adopting the euro.

Don't panic if you forget to use up old European currencies before you return to the United States.

Thomas Cook will redeem them for dollars at its 40 foreign exchange bureaus in the United States, as long as the individual country's central bank accepts them, said David Montgomery, general manager of North American retail operations. American Express's 120 U.S. bureaus also will buy them for dollars for years to come.

For instance, French francs and German marks will be redeemed indefinitely by their central banks, Italian lire and Greek drachma until 2012, and Dutch guilders until 2032.

Citibank, for its part, will redeem local currencies until Feb. 28 at its U.S. branches and two foreign exchange bureaus in Manhattan, spokeswoman Maria Mendler said.

Many travelers look forward to the convenience of a currency whose value is close to the dollar, with one euro trading at about 90 cents on foreign exchange markets last week.

Gerry Mullany, a New York Times editor who lives in the Brooklyn borough of New York City, recalls traveling to Italy last year trying to figure out if he was paying too many lire, which trades today at about 2,200 to the dollar.

``When we were in Italy, it was like 4,000 lire for a cup of coffee. We had to just sit down and figure out, `Gee, is that worth buying?''' said Mullany, who plans to travel in March to Belgium and France with his wife and 7-year old daughter.

The states adopting the euro are: Austria, Belgium, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain. Those staying out are Britain, Sweden and Denmark.