What factors weakened OPEC's position in the mid-1980s?

One problem that weakened OPEC was quota cheating by members of OPEC. Countries exceeded the agreed upon amount in order to gain more money. Other sources of oil competed with OPEC oil as well. While Middle Eastern oil was important, it wasn't the only source. Saudi Arabia also let OPEC know that it was not prepared to lose in the market share. It was willing to flood the market in order to maintain its position.