Here you see another of my lousy charts where you see oil prices per month since 1983.
Venezuela's oil is usually cheaper than the average OPEC, WTI or Brent. The first bar indicates 1990. During most of that decade the average oil price was below $20 per barrel. Chavez got there when oil prices were the lowest for over a decade. Chavez still has a lot of resources at his disposal, but he cannot afford for long prices under 40. Venezuela's population has increased since 1998 in at least 6 million people and Chavez has to pay loyalties to many more in Venezuela and above all abroad.