PARIS — When Sylvia Johnson started looking for a two-bedroom apartment in a fashionable quarter near the Park Monceau, she thought she could buy something for about $1.2 million. Wrong.

She had to raise her budget by about $500,000 — a bit of a shock for someone from Louisville, Ky., where home prices rose about 2 percent last year.

"Ideally, I would have gotten in two years ago and really made a big gain," says Johnson, 55, a retired healthcare consultant.

The housing boom is not just a U.S. phenomenon: It's a global boom. Some real-estate markets around the world are making the U.S. market look calm. In France, prices have risen 87 percent since 1997, vs. 73 percent in the U.S. Real-estate prices are up 154 percent in Britain, 145 percent in Spain and 192 percent in Ireland over the same period, according to The Economist.

The feeding frenzy is being driven by low interest rates, which are even lower in Western Europe than in America. In addition, many Europeans are getting their first taste of American-style mortgage loans, making it easier for buyers to afford homes at rising prices. Real estate also might look like a more stable investment to people who got burned in the stock market bubble. And the rally this spring in the value of the U.S. dollar has brought many Americans to Europe in search of exotic real-estate investments.

This is the longest international real-estate boom ever, and that's making people nervous.

"One thing which is quite amazing is the length of time," says Thomas Helbling, an economist for the International Monetary Fund. "It roughly started between 1995 and 1997, depending on the country. And with the exception for the moment of Australia and the U.K., where markets have turned, it's been going on 10 years."

Of course, not every market is on fire. Home prices in Germany are tethered to the country's double-digit unemployment rate and depressed consumer confidence levels, and in Britain prices have peaked and appear beyond the reach of many buyers.

Stuart Twells, a nurse in London, says he's thinking about getting out of the profession because on his salary, he can't even afford to buy a studio apartment, which he says would cost almost $300,000.

"I've been looking into a driving job — taxi driving, train driving — or trade or to carry on in nursing but go into pharmaceutical sales," he says.

Short-term interest rates — which influence mortgage rates and other consumer loans — are a meager 2 percent in Europe and expected to decline in the coming months. In the U.S., by contrast, the Federal Reserve last month raised rates for its target for short-term interest rates to 3.25 percent, the highest in almost four years. (Mortgage rates across the Atlantic are difficult to compare, generally, because they vary from country to country, depending on the level of competition between banks and the rates of inflation.)

What's more, European banks are finally getting the hang of U.S.-style mortgage loans. As prices really shot up about two years ago, banks started offering more flexible-interest and interest-only loans, as well as loans lasting up to 35 years. Previously, the standard home loan in Europe was a 15-year, fixed-rate mortgage. Banks "had to make it easier for people to buy homes because prices were rising so quickly," says Patrice Brunet, director of Talleyrand, a real-estate company in Paris.