BOSTON -- Billionaire investor Steven A. Cohen's SAC Capital Advisors returned 20.10 percent this year, delivering some of the industry's best returns, even as his hedge fund pleaded guilty to insider trading charges and prepared to return outside capital.

The fund reported to outside investors late Monday that it gained 1.88 percent between December 1 and December 27, a source familiar with the numbers said.

A spokesman for the fund declined to comment.