SAN FRANCISCO  For months, Google has promised investors that the company’s online advertising system would do relatively well in an economic downturn. On Thursday, it showed evidence that it may be able to deliver on that promise.

Google said that its growth rate continued to slow in the third quarter. But the company fared better than Wall Street expected as it reported a solid 26 percent jump in net income to $1.35 billion, or $4.24 a share, from $1.07 billion in the third quarter of 2007. The company’s results were bolstered by strong gains in online advertising and efforts by Google to slow hiring and rein in costs.

Google’s shares, which rose to $353.02, or 4 percent, in regular trading on Thursday, jumped another 10 percent after the company reported its financial results. However, they remain down sharply from their high of just over $740 last November.

Google’s chief executive, Eric E. Schmidt, said the results reflected marketers’ acceptance of a system that is better and more measurable than other forms of advertising. He said that while the economic environment was unpredictable, Google was poised to continue doing relatively well.