Until 1972, the price was below $20/bbl. In 1999, the price dipped briefly to about $13/bbl (Asian economic crisis), by in 2000 it was back to over $20/bbl. The upward climb began in approx. 2003, up to $60/bbl in 2006.
The median price has been $26.50 over the period 1970-present. Charts and history at WTRG:
Oil price history

The major oil companies do not dominate oil production and prices; state-owned oil and the futures market call the tune today. Like all commodity prices, there are wide swings in prices.

OPEC was founded in 1960 with five members, Iran, Iraq, Kuwait, Saudi Arabia and Venezuela. By 1971, Qatar, United Arab Emirates, Indonesia, Libya, Algeria and Nigeria joined OPEC.

The WTRG website linked above gives a detailed analysis of oil prices and the reasons for price shifts. A fascinating story.