Last week, we learned that the Securities and Exchange Commission was investigating secondary markets for stock trading, where investors buy and sell shares of privately held companies. This week, of course, news hit that Facebook was selling a sizable chunk of its privately-held company to Goldman Sachs, which will distribute it to its wealthy clients. While off-exchange stock trading might sound like a relatively new phenomenon, it's already grown to be a very significant part of the market. Jacob Bunge from the Wall Street Journal reports:

Private markets accounted for a record 1 in 3 U.S. stock trades last month as the country's four largest stock-exchange groups continued to lose market share, according to data released Monday.

The rise of so-called dark pools and other off-exchange strategies aimed at large banks and institutional traders comes as regulators on both sides of the Atlantic grapple with balancing the market efficiencies the alternative venues say they generate with the impact on individual investors.

No wonder the S.E.C. has become interested. One-third is a huge portion of trades, and as financial regulations grow stricter, such transactions aren't likely to lessen. While average Americans generally have a tough time beating financial professionals when it comes to investing, if this trend continues, it may become even more difficult.

Read the full story at the Wall Street Journal.