A benchmark index used in the oil industry that was created by the Philadelphia Stock Exchange (PHLX), where it trades. The Oil Service Sector Index is a price-weighted index composed of the common stocks of 15 companies that provide oil drilling and production services, oil field equipment, support services, and geophysical/reservoir services. The OSX was set to an initial value of 75 on December 31, 1996. Options began trading on February 24, 1997.