Preparations for the jumbo stock market debut of Glencore International took a big step forward Thursday when the commodities producer and trader formally announced its intention to float on the London and Hong Kong stock exchanges later this year.

Glencore, which is based in the Swiss town of Baar and employs nearly 58,000 people around the world, is aiming to float a stake of up to 20 percent.

The main offer could raise as much as $11 billion, the bulk of that in London.

That amount could be beefed up by another 10 percent if good demand allows for more shares to be sold, Glencore said in a statement declaring its intentions.

With a potential value of as much as $12.1 billion, the initial public offering could be the biggest in the world this year and will be closely watched in a market that remains intensely nervous about the unrest in the Middle East and North Africa and the lingering debt woes of several European countries.

A surge in the price of oil and many other raw materials that has also fanned market nervousness, however, is favorable from the perspective of Glencore, whose main activity is trading metals, minerals, oil, coal and grains.

By staging a secondary listing in Hong Kong, Glencore is also hoping to tap into a marketplace that has gained huge significance in recent years.

Hong Kong now attracts a majority of global I.P.O. volumes, largely thanks to a flood of mainland Chinese companies choosing to go public.

However, non-Asian companies are also increasingly choosing to list in Hong Kong and on other exchanges in the Asia-Pacific region, in a bid to tap into a cash-rich investor base and to raise their profiles in a part of the world that is becoming increasingly important to global companies.

Prada, the Italian luxury goods company, is preparing to list in Hong Kong around the middle of the year.

Founded in 1974, Glencore is a closely held company owned by its employees and management. It also owns slightly more than a third of the global mining giant Xstrata.

‘‘An I.P.O. is the next logical step in our development and strategy,’’ Ivan Glasenberg, the chief executive, said in the statement. ‘‘It will provide us with the financial flexibility to capitalize upon long-term growth opportunities throughout our business and achieve further sustainable growth.’’

Glencore intends to use about $5 billion of the I.P.O. proceeds for capital expenditures over the next three years.

Citigroup, Credit Suisse and Morgan Stanley are the joint global coordinators for the issue.

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