SHANGHAI  China is taking advantage of the economic downturn to go on a major shopping spree, investing in energy and other natural resources that could give it an economic advantage it has never had before.

Some economic analysts say they believe that China’s investments pose a threat to competitors like the United States. In the last move, Beijing said on Friday that one of its big state-owned banks, the China Development Bank, would lend the Brazilian oil giant Petrobras $10 billion in exchange for a long-term commitment to send oil to China.

China signed similar deals this week with Russia and Venezuela, bringing Beijing’s total oil investments this month to $41 billion. They represent an important investment. Supplies of commodities like oil are likely to tighten again once global growth picks up, and China will have a toehold it lacked during the recent boom, when it grew phenomenally even with limited access to resources.

But some analysts say China’s recent investments are welcome because they will help finance much-needed development, increasing the global supply of oil and natural resources at a time when many of the world’s biggest banks are reluctant to lend.