There are still a couple of days left in which things could turn around, but as it stands, it looks like the biggest loser in the S&P 500 this year will be Chesapeake Energy. The Oklahoma City-based energy exploration company opened the year at 19.42 but tumbled along with oil prices throughout the year. It's now at 4.07 - losing 79 percent of its value in a single year.
Close behind Chesapeake were a couple of other oil & gas stocks. Southwestern Energy has lost 75 percent of its value this year, and Consol Energy has lost 74 percent. All told, the S&P 500's energy sector is down 22 percent for 2015.
The biggest loser not in the energy sector was Freeport-McMoRan, which has lost 67 percent of its value. Although it's technically in the materials sector because of its extensive mining operations, Freeport also is involved in the oil & gas industry.