Consumers from California to Switzerland are developing a taste for dark chocolate, taking a bite out of global cocoa supplies and driving up candy prices in both high-end boutiques and mass-market drugstores.

The cost of one kilogram of chocolate in the U.S. is expected to hit a record $12.25 this year, a 45% increase from 2007, according to market-research firm Euromonitor International.

Prices are on the rise because of a shortage of cocoa beans, which are roasted and ground to make chocolate. Market experts estimate supplies will fall short of demand this year for the first time since 2010 after dry weather is expected to hurt the next harvest in West Africa, where 70% of cocoa beans are produced.

The supply shortfall is emerging just as Americans and Europeans are buying more chocolate, particularly the darker varieties, for both health and economic reasons. Dark chocolate often requires more cocoa beans per ounce than milk chocolate, which means that even small shifts in buying trends can have a big impact on the $5.4 billion cocoa-futures market, traders and investors say.

Cocoa prices are up 21% so far in the third quarter, outperforming broad commodity indexes. Hedge funds and other money managers are making bullish bets on cocoa futures in unprecedented numbers, wagering that steady economic growth in the world's developed economies will continue to fuel the rally. Big consumption gains in emerging markets such as Brazil also are lending support to prices.

Recent chocolate-sales figures reveal 'a better-than-expected recovery in core markets such as North America and Northern Europe,' said Jonathan Parkman, head of agriculture at Marex Spectron, a commodities brokerage based in London. 'The return of confidence has allowed the consumer to buy a bit more of the premium-brand chocolates.'

This year, total U.S. chocolate consumption is expected to rise for the first time since 2008, according to Euromonitor. Demand is seen rising in Western Europe for the fourth straight year.

'People are going back to an impulse buy,' said Kip Walk, head of sustainability at Blommer Chocolate Co., which manufactures chocolate for food companies. Mr. Walk said the rebound in demand for premium chocolate reflects the pent-up demand that continues to recover from the global financial crisis.

'Chocolate was resilient but not recession-proof,' he said. 'The very high-end products got the brunt of' consumption declines during the recession.

Dark chocolate is behind most of that new demand, according to NPD Group, a market-research firm based in Port Washington, N.Y.

Dark chocolate's share of the U.S. market for chocolate bars will approach 20% this year, from just over 18% in 2008, according to Euromonitor. In Switzerland, where per-capita chocolate consumption is among the world's highest, the share of dark chocolate jumped to 30% from 22% over the same period.

'There's a general trend toward the dark chocolate,' said Nicholas Fereday, a food-industry analyst at Rabobank. 'The benefit of having the high cocoa content is having a lower sugar content and that's what would appeal to calorie-counters.'

Earlier this month, the European Commission said Swiss chocolate maker Barry Callebaut AG (BARN.EB) could legallyadvertise that consumption of one of its chocolate products, Acticoa, could help maintainhealthy blood circulation.

Recent converts to dark chocolate say they have been won over by heavily advertised health benefits and its lower sugar content compared with milk chocolate.

'As I got older I liked dark chocolate better, knowing that there's more nutritional value than milk [chocolate],' said Charlotte Vance, a 22-year-old from Los Angeles, who is studying to be a nutritionist.

Candy makers have noticed the shift. Hershey Co. (HSY), the biggest U.S. candy maker by sales, has been broadening its product lineup to include gourmet brands such as Dagoba and Scharffen Berger and dark-chocolate versions of brands like Kit-Kat and Reese's Peanut Butter Cups.

In 2012, Hershey acquired the Canadian company that manufactures Brookside-branded candy, dark chocolate with juices made from fruits such as acai and pomegranate.

Hershey and other companies are seeking to capitalize on tastes of consumers such as Dwayne Seegar, 38, who works in administration in New York. Mr. Seegar has preferred dark chocolate since he was a kid.

'Lately I find the higher the percent [cocoa content] the more I like it,' he said.

The taste isn't for everyone.

'Milk [chocolate] has that creamyaspect that's more appealing to my palate,' says Jake Poteat, 23, a graduate student at New York University.

And some investors believe the rally in cocoa futures is overblown. The outlook for West African supplies is too pessimistic, and cocoa prices are likely to fall back once the harvest there begins around mid-October and traders get more precise indications of actual output, said Shawn Hackett, president of brokerage and consulting firm Hackett Financial Advisors in Boynton Beach, Fla.

The cocoa-futures market is experiencing a 'feeding frenzy,' Mr. Hackett said. 'This has all the elements of [speculators] getting carried away.'

Still, the focus remains on rising demand, especially ahead of the confectioners' quartet of Halloween, Christmas, Valentine's Day and Easter in the U.S. Cocoa prices soared to a one-year high last week, though on Friday they slipped 0.8% to $2,608 a metric ton as investors booked profits.

On Friday, the U.S. Commodity Futures Trading Commission reported that, as a group, money managers had placed $1.72 billion of bullish bets on cocoa as of Sept. 17. The number of these so-called net long positions, 65,609, is the biggest since at least 2006, when the U.S. commodities regulator began reporting this data in its current form.

Industry executives say it is likely that, if sustained, the move in cocoa futures will result in even-higher chocolate prices.