* Retail daily average trades up 8 percent
* Client assets rise 11 pct from a year earlier
* Sandler O'Neill raises EPS estimate
* Shares rise 1.5 pct (Adds acquisition details; updates shares)
SAN FRANCISCO, May 18 (Reuters) - OptionsXpress Holdings Inc OXPS.O, an online broker being acquired by Charles Schwab Corp (SCHW.N), said on Wednesday that April retail trading activity increased an average 8 percent from a year earlier.
The increase bucks a trend of declining April trading at the three major online brokers, Schwab, TD Ameritrade Holding Corp (AMTD.O) and E*Trade Financial Corp (ETFC.O), which together reported an average 2.3 percent decline in April daily average trades.
Shares of optionsXpress rose 27 cents, or 1.5 percent, to $17.84 on Nasdaq. Schwab gained 1.7 percent to $17.65.
Schwab agreed to buy optionsXpress in March in a $1 billion all-stock deal that valued optionsXpress at $17.91 per share, 17 percent more than its closing price on the trading day before the acquisition was announced.
Chicago-based optionsXpress said on Wednesday that client assets stood at $8.7 billion at the end of April, 11 percent higher than a year earlier and up 3 percent from March.
Daily average trades are a widely watched measure of client confidence in the market and may portend higher revenue for firms. Retail average daily revenue trades at optionsXpress rose to 36,100 in April, up 2 percent from March.
Sandler O'Neill analyst Richard Repetto on Wednesday raised his second-quarter earnings estimate for optionsXpress to 26 cents per share from 23 cents, citing the higher retail trading volumes.
San Francisco-based Schwab's move to buy optionsXpress would give it some of the most active retail traders in the booming options market. TD Ameritrade bought options specialist thinkorswim in 2009, also to gain more options traders. [ID:nN21283754]
OptionsXpress expects the acquisition to be completed in the third quarter.
The prevalence of Web-based brokers, their investor-education drives and a move to electronic markets have helped increase trading in options, which give contract holders the right to buy or sell an underlying security over an agreed time, or at a set date. (Reporting by Philipp Gollner; Editing by Steve Orlofsky and Gerald E. McCormick)