(Adds Schwab data, updates stock prices)

Knight Capital Group Inc.'s (NITE) August U.S. average daily trading volume climbed 7.7% from July on a dollar basis and surged 53% from a year earlier, while Charles Schwab Corp. (SCHW) reported a 24% rise from last year.

Investors continue to return to the market as the major stock indexes strengthen. Although Schwab Chief Financial Officer Joe Martinetto found the results encouraging, he noted that revenue is under additional near-term pressure as trading activity lags second-quarter levels and short-term interest rates continue to fall.

Average daily trading volume handled by Schwab jumped 15% in August from July to 334,000. Total client assets rose 3% during the month as stock markets continued to rise and as net inflows were $8.5 billion. The company had 61,000 new brokerage accounts, up 5% from July, and 7.6 million in total.

Martinetto said he expects fee waivers resulting from declining yields in the company's money market mutual funds to rise to $80 million in the third quarter from $30 million in the prior quarter. As a result, the company expects asset-management and administration fees to drop sequentially by up to 8% to 10%. Lower rates also have reduced investment portfolio yields, which could result in a 2% to 4% reduction in third-quarter net interest revenue. Meanwhile, average daily trading volume handled by Knight rose 5.4% in August from July to 4 million shares and doubled the year-earlier figure.

Knight Chairman and Chief Executive Thomas M. Joyce noted August saw U.S. equities markets remain in a summer slowdown despite higher trading activity in "a handful of low-priced, financial stocks." At Knight, a diversified order flow "managed to sustain our trade volumes during the seasonal pause in activity," Joyce said.

Knight Capital's results have been boosted in recent months by higher volumes, particularly as its global-markets business gains market share. Many stock-trading firms saw volume gains even as stocks were heading lower last year, as investors generally fled positions, leading to market volatility.

Knight Capital's shares were down 0.9% to $21.60 while Schwab was off 2.2% at $17.96.

-By Mike Barris, Dow Jones Newswires; 212-416-2330; mike.barris@dowjones.com