The wealthiest 1 percent now control 39 percent of the world's wealth, and their share is likely to grow in the coming years, according to a new report.

The world's total private wealth grew 7.8 percent last year to $135 trillion, according to the Boston Consulting Group's Global Wealth report. The top 1 percent control $52.8 trillion, and those worth $5 million or more control nearly a quarter of the world's wealth.

That concentration is likely to increase in the coming years as the wealth of the wealthy grows faster than overall global wealth. The number of millionaires in the world surged by 10 percent year, reaching 13.8 million. The study predicts that global wealth will grow around 4.8 percent a year over the next five years—though millionaires will see their wealth grow nearly twice as fast.

Those worth $5 million or more will see their wealth grow 8 percent, while those worth more than $100 million will see their wealth grow 9.2 percent. The $100-million-plus group will see their share of global wealth grow to 6.8 percent in 2017 from the current 5.5 percent.

What's driving the wealth of the wealthy? It depends on the country. In the developed world—the U.S. and Europe— it's mainly stocks. And stocks have been on a tear this year in the U.S., which has mainly benefited the top 5 percent, who own 60 percent of all individually held stocks.

(Read More: Surging Stock Market Cheers Up the Rich)

In developing markets, the main wealth creator is economic growth and savings. Yet the amount of wealth held in stocks and in offshore wealth (again mainly held by the wealthy) in developing countries is also growing. The amount of wealth held in equities in Asia (excluding Japan) surged by 21.9 percent in 2012.